msm: sde: avoid segmentation of dma_buf mappings

Ensure dma_buf mappings aren't broken in to multiple segments
by setting the devices segment size and boundary.  This will
improve performance and the sg_dma_len() API will now give
the full buffer size.

Change-Id: Ic8a6ac00e839255bee8b9fb09362b4a5c51d1f83
Signed-off-by: Steve Cohen <cohens@codeaurora.org>