msm: mdss: enable source split with dual-dsi partial update

Enable source split with dual-dsi partial update. When source split
is used, it is a HW requirement that both layer mixer (LM) width be
of same size. Based on this requirement validate ROIs passed by
user program for the correctness and program the MDP HW and display
panel according to the ROIs. In order to simplify the logic, whenever
source split is enabled, dual-dsi or not, user program will always
sent merged ROI through l_roi during commit IOCTL.

Change-Id: Ic07deab12aa43bc4f61762303ed367fe3131389f
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>