This commit brings in basic support fo the i.MX RT 1050 'crossover' SoC. The...

This commit brings in basic support fo the i.MX RT 1050 'crossover' SoC.  The basic support is complete and compiles without error, but is still untested.

This port was the joing effort of Janne Rosberg, Ivan Ucherdzhiev, and myself.  I give credit to Ivan for the kill because he is the one to held on to the end.

Squashed commit of the following:

  Author: Gregory Nutt <gnutt@nuttx.org>
    configs/imxrt1050-evk/scripts:  Add section to linker script to handle the case where RAMFUNCs are enabled.  RAMFUNCs appear to be enabled in the default configuration ... they probably should not be enabled.

  Author: Ivan Ucherdzhiev <ivanucherdjiev@gmail.com>
    arch/arm/src/imxrt:  imxrt_lowputc.c is finished. Now everything needed for the initial port is done and ready for testing.
    arch/arm/src/imxrt:  Add logic to imxrt_lowputc.c.  Still incomplete.

  Author: Ivan Ucherdzhiev <ivanucherdjiev@gmail.com>
    arch/arm/src/imxrt:  Add serial support.  configs/imxrt1050-evk:  Add linker script.

  Author: Gregory Nutt <gnutt@nuttx.org>
    arch/arm/src/imxrt:  Add initial cut at imxrt_allocateheap.c

  Author: Ivan Ucherdzhiev <ivanucherdjiev@gmail.com>
    arm/arm/src/imxrt:  Completes all definitions for PADMUX, CTLMUX, and IOMUX_INPUT and mapping tables on imxrt_gpio.c and imxr_iomuxc.c.
    arch/arm/src/imxrt/chip:  Add definitions for IMXRT_PADCTL and IMXRT_PADMUX registers.  Only the IMXRT_INPUT definitions in this commit.
    arch/arm/src/imxrt/chip:  Add more IOMUXC register definitions.

  Author: Gregory Nutt <gnutt@nuttx.org>
    configs/imxrt1050-evk:  Add STRIP definition to Make.defs.
    arch/arm/src/imxrt:  Bring in i.MX6 memory configuration settings.
    arch/arm/src/imxrt:  Remove call to non-existent imxrt_gpioinit() from imxrt_start.c.
    arch/arm/src/imxrt:  Bring in incomplete imxrt_iomuxc.c file from i.mx6.
    arch/arm/src/imxrt:  Add first cut at GPIO interrupt logic.
    arch/arm/include:  Add definitions to support a second level of GPIO pin interrupts.

  Author: Janne Rosberg <janne.rosberg@offcode.fi>
    arch/arm/src/imxrt:  Add imxrt_wdog.c/.h

  Author: Gregory Nutt <gnutt@nuttx.org>
    arch/arm/src/imxrt:  Port SAMv7 interrupt logic to imxrt_irq.c.
    arch/arm/src/imxrt:  More clarification of the start-up memory map.
    arch/arm/src/imxrt:  Some mostly cosmetic clean-up to the imxrt_start.c file that was so rudely taken from the SAMv7.
    arch/arm/src/imxrt:  Add imxrt_start.c.  Initial commit is the the SAMv7 startup logic with name changes.

  Author: Ivan Ucherdzhiev <ivanucherdjiev@gmail.com>
    arch/arm/src/imxrt:  Adds a few IOMUXC register definitions.

  Author: Janne Rosberg <janne.rosberg@offcode.fi>
    arch/arm/src/imxrt:  Add imxrt_clockconfig.c/.h
    configs/imxrt1050-evk:  Add clock configuration definitions to board.h
    arch/arm/src/imxrt:  Fix CCM register name; Fix doubly defined in LPUART bit field.
    arch/arm/src/imxrt:  Add analog defines to CCM register definition header file.

  Author: Gregory Nutt <gnutt@nuttx.org>
    arch/arm/src/imxrt:  Bring in GPIO C files from i.MX6.  Things are in disarray now because that GPIO logic depends on IOMUXC logic which is not yet in place.
    arch/arm/src/imxrt:  Add a few more GPIO definitions to make the header file compatible with i.MX6
    arch/arm/src/imxrt/chip:  Add GPIO register definition file.

  Author: Janne Rosberg <janne.rosberg@offcode.fi>
    arch/arm/src/imxrt:  Add DCDC register definitions.
    arch/arm/srch/imxrt: Add CCM register bit definitions

  Author: Gregory Nutt <gnutt@nuttx.org>
    Purely cosmetic
    arch/arm/src/imxrt:  Add system reset controller register definition header file.
    Embarassingly trivial change left in compiler.
    arch/arm/src/imxrt:  Finishes i.MX RT1050 LPUART register definition header file.
    arch/arm/src/imxrt:  Beginning of an i.MX RT1050 LPUART register definition header file.
    Some trivial things

  Author: Janne Rosberg <janne.rosberg@offcode.fi>
    arch/arm/src/imxrt:  Add imxrt_wdog.h
    arch/arm/src/imxrt:  Add initial imxrt_ccm.h

  Author: Gregory Nutt <gnutt@nuttx.org>
    Trivial update to README.
    arch/arm/src/imxrt:  The i.MX Rt implements 4 bits of interrupt priority, not two.  Thanks, Janne.
    arch/arm/src/imxrt:  Fix some initial compile issues.  Still a long way from complete, but there is a buildable environment now for the imxrt1050-evk.
    configs/imxrt1050-evk:  Add an initial NSH configuration for testing.
    configs/Kconfig:  Hook the i.MX RT 1050 board configuration into the NuttX configuration system.
    configs/imxrt_evk:  Add the framework for i.MX RT 1050 board support.
    arch/arm/src/imxrt:  Bring in a few more files from LPC54xxx.
    arch/arm/src/imxrt:  Bring in imxrt_clrpend() from the LPC54xxx.
    arch/arm/src/imxrt:  Bring in Cortex-M7 SysTick setup from the SAMv7.
    arch/arm/src/imxrt:  Add a few easy files.
    arch/arm/src/imxrt/chip:  Add memory map header files.
    arch/arm/src/imxrt:  A few basic files to start the port to the i.MX RT 1050.