dmaengine: Driver for Topcliff PCH DMA controller

Topcliff PCH is the platform controller hub that is going to
be used in Intel's upcoming general embedded platforms. This
adds the driver for Topcliff PCH DMA controller. The DMA
channels are strictly for device to host or host to device
transfers and cannot be used for generic memcpy.

Signed-off-by: Yong Wang <yong.y.wang@intel.com>
[kill GFP_ATOMIC, kill __raw_{read|write}l, locking fixlet]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>