drm/msm/sde: use the drm API for populating rect coordinates

DRM framework provides an API for populating src and dst rects.
This patch updates SDE to use the new API.

Change-Id: Ic4ab10a0c91f0be528f7c3dc19325ce17f33ebc2
Signed-off-by: Steve Cohen <cohens@codeaurora.org>