dmaengine: mpc512x: add support for peripheral transfers

Introduce support for slave s/g transfer preparation and the associated
device control callback in the MPC512x DMA controller driver, which adds
support for data transfers between memory and peripheral I/O to the
previously supported mem-to-mem transfers.

Signed-off-by: Alexander Popov <a13xp0p0v88@gmail.com>
[fixed subsytem name]
Signed-off-by: Vinod Koul <vinod.koul@intel.com>