drivers: Add Atmel SAM DAC (DACC) driver

Add Digital-to-Analog Converter driver (based on DACC module) for Atmel
SAM MCU family. Only SAME70, SAMV71 series devices are supported in
this version.

Tested on Atmel SMART SAM E70 Xplained board.

Origin: Original

Signed-off-by: Piotr Mienkowski <piotr.mienkowski@gmail.com>