Add patches for ADC peripherals

Add a patch to fixup a few registers in the ADC peripheral
for ATmega328P, ATmega32U4, ATmega1280, and ATmega64.

Add patch for SPI device

atmega1280: Add remaining common patches

atmega1280: Factor out USART into a common patch

Signed-off-by: Rahix <rahix@rahix.de>

Add USART1 patch to atmega1280.