dmaengine: mv_xor_v2: add support for suspend/resume

This commit adds the support for suspend/resume in the mv_xor_v2
driver. The suspend suspend function disables the XOR engine after the
DMA stack has handled all pending descriptors in the queue. The resume
function re-configures the XOR engine and re-enables the engine.

Signed-off-by: Hanna Hawa <hannah@marvell.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>