msm: kgsl: Set DMA Mask for gmu device

A single page buffer allocated via dma_alloc_attrs comes
from the system memory instead of contiguous space now.
That page can have address larger than the default dma
mask of 32 bits.

Change-Id: I591f09362d67b2a80e335ba3e593bd5e4e2f08ea
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>