Add support for a generic windows-based EABI toolchain; Add NX configuration to force default NXTK border colors

Correct border colors for SAM3U-EK border; clean up some comments; make sure that sam_vectors.S is identical to stam32_vectors.S

Remove CONFIG_XYZ_BUILTIN configurations, replace with the single CONFIG_NSH_BUILTIN_APPS.  Add SAM3/4 sam_periphclks.h which is just a header file that includes the right header file.  Misc SAM3U-EK cleanup

Beginning updates of SAM3U header files o include support for the SAM4S: WDT, SUPC, EEFC, MATRIX, and PMC

SAM4L: Add logic to enable selected peripherals on power up; Extend configuration so that each peripheral can be selected -- even though the drivers are not yet implemented

Fix a backward conditional that cause the STM32 usb host driver to fail to detect disconnection events.  From Scott

Add flow control support to the STM32 serial driver; Fix some issues with UART2 and 5.  From Lorenz Meier and Mike Smith

Add register definitions for SAM4L BPM and SCIF blocks; SAM4L clock initialization now selects an optimal  power scaling mode