NxWM::CCalibration: Add logic to collect and average samples, optionally discarding the most extreem values

Misc changes to README files; Update SAMA5D3x-EK NxWM configuration to use Calibration instruction messages

SAMA5 LCDC:  Correct how framebuffer memory was being mapped; Remove options to get framebuffer memory in various.  Because of the mapping and aligment requirements, those options really cannot be supported

SAMA5 LCDC:  Wait when the LCDC is resynchronizing (SIF); Try start-up parameters from Barebox (this still don't work)

SAMA5 LCDC: Default resolution if now RGB565; Add option to select a different output resolution than the sofware resolution (needs to the 24BPP for this LCD).

SAMA5 LCDC: Move DMA descriptors out of internal SRAM and into SDRAM. I am not completely clear, but it looks like the LCDC cannot support DMA from internal SRAM

Add option to enable Aduino Due specific logic, like pull-up on UART0 RXD.  Suggested by gdi@embedders.org

Add framework for Spark Core board support.  The initial commit is a clone of the Maple Mini and still needs Spark customizations

Add freedom-kl25z/minnsh configuration:  This is an experiment to see just how small we and get an NSH configuration.  From Alan Carvalho de Assis.

KL25Z:  Add low-level up_lowgetc function that can be used to provide an NSH console when the file system (and hence the serial driver) is disabled.  From Alan Carvalho de Assis

The last checkin replaced some impossible error handling with DEBUGASSERT.  Except that one of the case is actually possible in one cornercase and had to be restored

Mov apps/examples/composite to apps/system/composite; convert configs/stm3210e-eval/composite to use kconfig-frontend tools -- untested