Add instructions to enable RTC in the nsh/ configuration; RTC enabled by default in the demo configuration

SAMA5 LCD:  Move framebuffers to center of free memory region.  That creates a guard band around the framebuffers that gives a little protection from any bad writes into the framebuffer

Minor tweaks to debug output; started renaming some icons to include size in the name; SAMA5 NxWM config needs libm

New touchscreen scaling algorithm for the case where measured X values vary with y position (and vice versa)

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