msm: kgsl: allow dma-bufs to be mapped by user address

Allow a userspace pointer to a dma-buf to be mapped by
IOCTL_KGSL_MAP_USER_MEM with KGSL_USER_MEM_TYPE_ADDR,
with the correct dma-buf handling.

CRs-Fixed: 607830
Change-Id: I037ed070b96592040328014c9adbd8a5b4d4191f
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>