arch-atmega Kconfig: new option RUN_BOOTLOADER_ON_1200_BPS

RUN_BOOTLOADER_ON_1200_BPS is an option which makes configurable the
behaviour implemented for Arduino IDE compatibility.
(see previous commit d14fa291)

Signed-off-by: Aurelio Colosimo <aurelio@aureliocolosimo.it>
tasks: yun-gpios.cfg 'NC' gpios replaced by their name on chip

Signed-off-by: Aurelio Colosimo <aurelio@aureliocolosimo.it>