dma: Add MPC512x DMA driver

Adds initial version of MPC512x DMA driver.
Only memory to memory transfers are currenly supported.

Signed-off-by: Piotr Ziecik <kosmo@semihalf.com>
Signed-off-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: John Rigby <jcrigby@gmail.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>