PIC32MZ: Make sure that the microMIPS ISA is selected on all common MIPS32 assembly files when the PIC21MZ is selected

MIPS:  Add some build support for the M14K and also for the PIC32MZ Starter Kit.  Still a long way to go

STM32: Fix for compilation introduced by last backup RAM change.  Not sure it it is correct, be now things do compile

Adds the ability to use the STM32F2 and STM32F4 Battery Backedup SRAM in the file system. With an option to Save Panic context to one of the files. From David Sidrane.

Changes to support fully write protecting the backup domain. N.B. stm32_pwr_enablebkp did not account for the delay from enable to the domain being writable. The KISS solution is a up_udelay. A more complex solution would be a negated write test with restore.  From David Sidrane.

Tiva: Move GPIIO prototypes out of arch/arm/include/tiva/irq.h to arch/arm/tiva/tiva_gpio.h where they belong

Fix some time value changes; mostly changing greater than 1000000000 to greater than or equal to 1000000000.  From Juha Niskanen

VFS: The inode unlink method should not be support if operations on the root pseudo-filesystem are disabled.

Tiva: Updated files to allow for ADC triggering by the timer. I’ve cleaned up some parts of the ADC code, too, and fleshed out the PWM triggering ioctl.  From Calvin Maguranis

Break out a new internal interface, stm32_rtc_setdatetime().  This eliminates some un-necessary time conversions.  From Freddie Chopin.

Add a skeleton implementation of the RTC lower half interface at arch/arm/src/stm32/stm32_rtc_lowerhalf.c.  This is just the framework for the RTC lower half.  None of the interface methods have yet been implemetned.