drm/msm: Drop local dma_parms

Since commit 9495b7e9 ("driver core: platform: Initialize dma_parms
for platform devices"), struct platform_device already provides a
dma_parms structure, so we can save allocating another one.

Also the DMA segment size is simply a size, not a bitmask.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>