Merge arduino-nano-168 into arduino-nano (differences are minimal)

src/arch/arduino-nano-168/Kconfig

src/arch/arduino-nano-168/Makefile.inc

src/arch/arduino-nano-168/arch.cc

src/arch/arduino-nano-168/driver

src/arch/arduino-nano-168/prompt

src/arch/arduino-nano/Kconfig

src/arch/arduino-nano/Makefile.inc