arch/arm/src/lpc54628:  With these changes, the LPCXpresso-LPC54628 NSH configuration is fully functional.  Also adds a README file for the board.

configs/xtrs:  Removed the XTRS configuration This was an unverified port of NuttX to a TRS-80 simulator.  It was removed because (1) it is, as I said, unverified as well as unsupported, and (2) the TRS-80 simulation is a sub-optimal platform.  That platform includes a 16-bit ROM image and only a 48Kb RAM space.

configs/mx1ads:  This commit removes board support for the mx1ads board.  That board support was never completed and I no longer even have the hardware.  The unfinished board support is still available in the Obsoleted repository if anyone would ever like to resurrect it.

    BCM2708:  Add enough infrastructrue (more stubs) to get a clean compilation of the Pi Zero configuration (with many undefined things at link time).

    BCM2708:  Add basic interrupt handling logic

    BCM2708: Add interrupt register definitions.

    BCM2708:  Add irq.h header file

    BCM2708/Pi zero:  bcm_boot.c and bcm_memorymap.h now compile.  Added pizero linker script.

    BCM2708/Pi Zero:  Add Make.defs needed to build.

    arch/arm/include/bcm2708, arch/arm/src/bcm2708, configs/pizero:  Add some basic build and configuration logic.

    configs/pizero:  Add some basic structure of the Rasperry Pi Zero port.

    Created directory configs/pizero.  Nothing there now but a README.txt file.

    Add initial boot.c and memorymap.c files
    Author: Alan Carvalho de Assis <acassis@gmail.com>

    Add AUX/UART/SPI registers definition
    Author: Alan Carvalho de Assis <acassis@gmail.com>

    Pizero GPIO registers
    * Initial commit to add GPIO definitions
    * Add remaining GPIO registers definition
    Alan Carvalho de Assis <acassis@gmail.com>

    BCM2708 memory map:  Add VBASE defintions; fix VCSDRAM address per Alan; move all virtual address to the bottom of the file to avoid confusion -- top is all physical address; bottom is all veritural address.

    Add initial memory map to BCM2708/BCM2835
    Alan Carvalho de Assis <acassis@gmail.com>

Build System:  It is no longer necessary to have a unique Make.defs file for each configuration.  A board may share a common Make.defs file in the scripts directory.

configs:  Add readme for B-L465E-IOT01A Development kit.  This port is currently under consideration (but may not actually happen)

Revert "Add a placeholder for nucleo-64 boards.  Currently these are in various directories nucleo-f303re, nucleo-f334r8, and nucleo-l476rg but need to be consolidated here because these are all the same boards."

This reverts commit 935cc4e3.

Add a placeholder for nucleo-64 boards.  Currently these are in various directories nucleo-f303re, nucleo-f334r8, and nucleo-l476rg but need to be consolidated here because these are all the same boards.

Add configuration to prevent selection of Windows native toolchains when using Ubuntu under Windows 10