dmaengine: gpi: Set dma mask to 64

GPI driver need not consider the IOVA range and size when setting the
dma mask, which otherwise could result in a too low value for the mask
on 32-bit builds. Set it to 64 unconditionally.

Change-Id: I4ec1fb60dd6b62570b2c4a2b1f30c4349871d544
Signed-off-by: Siva Kumar Akkireddi <sivaa@codeaurora.org>