msm: msm_fb: Fix Regressions because of overmap changes.

Previous MDP overmap change is causing issues with HDMI because of
assumptions about overmap. This patch fixes all such issues.

Change-Id: Ifd2f8a0596d9df08538464bdcdd5946cf84db4d9
Signed-off-by: Vishnuvardhan Prodduturi <vproddut@codeaurora.org>