drivers: Add Atmel SAM DMA (XDMAC) driver

Added DMA (XDMAC) driver for Atmel SAM MCU family. The driver provides
private DMA API to be used by the SAM family device drivers. Public
DMA API to be used by user space programs is currently missing.

Tested on Atmel SMART SAM E70 Xplained board

Origin: Original

Jira: ZEP-1609
Signed-off-by: Piotr Mienkowski <piotr.mienkowski@gmail.com>