dmaengine: Add support for APM X-Gene SoC DMA engine driver

This patch implements the APM X-Gene SoC DMA engine driver. The APM X-Gene
SoC DMA engine consists of 4 DMA channels for performing DMA operations.
These DMA operations include memory copy, scatter-gather memory copy,
raid5 xor, and raid6 p+q offloading.

Signed-off-by: Rameshwar Prasad Sahu <rsahu@apm.com>
Signed-off-by: Loc Ho <lho@apm.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>