soc: atmel_sam0: Add support for SAMR34 and SAMR35 parts

Implement support for SAMR34 and SAMR35 parts, tested on a SAMR34
Xplained Pro dev board. Confirmed operational peripherals: UART, GPIO,
PWM, ADC.

NOTE: The SAMR34 datasheet lists NVIC line 20 for the ADC's interrupt,
but the SAML21 datasheet gives line 22. It appears that the SAMR34 sheet
is incorrect (the ADC doesn't function with line 20), and as such, I have
also omitted the adjustments for TC4 and AC...

Signed-off-by: Attie Grande <attie.grande@argentum-systems.co.uk>