drm/msm/sde: partial update of display output

Analyze the connector and crtc regions of interest and modify
the layer mixer output to match the user's desired output roi.
This patch adds SDE support for ROIs that are centered and
symmetric around the layer mixer split point.

Change-Id: I681a8e191a542b74b84fdb0d6d3542de3f332355
Signed-off-by: Lloyd Atkinson <latkinso@codeaurora.org>