Updates to README files
Move SAM3U header files to arch/arm/src/sam3u/chip. Some renaming of SAM3U to SAM to ssupport SAM4.  Convert all configs/sam3u-ek configurations to use the kconfig-frontends tool
Eliminated sam3u_internal.h. Use separate header files instead.  More renaming from sam3u_ to sam_ to make room in the namespce for the sam4l_
Add missing NSH configuration settings.  Correct some conditional logic for STM32 FALSH pre-fetch settings.  From Lorenz Meier
Rename sam3u/ architecture directories to sam34/ to include the SAM4L
Add dprintf() and vdprintf()