hwc: Partial update support for dual DSI panels with source
split.

1) When source split is enabled, both the panels are calibrated
   in a single coordinate system. So only one ROI is generated
   for the whole panel extending equally from the midpoint and
   populated for the left side.
2) Fixes a bug in mdpcomp where ROI generated for the frame is
   reset when a strategy fails.

Change-Id: I47fa0e827985dd76d06dcbe464ef832cfc57a671
3 files changed