liboverlay : Update magnification limit for MDP 400

Update liboverlay to address magnification limit for MDP 400.

MDP 400 has magnification limit of 8, and MDP 410 or later has a
magnification limit of 20.

CRs-Fixed: 413535
(cherry picked from commit df48275230f359af834d7292518aac2566aff524)

Conflicts:

	liboverlay/overlayCtrl.cpp
	liboverlay/overlayUtils.cpp

Change-Id: I809460080c467d60279aacdbd1e46e094a1fd525
Merge pull request #1 from CyanogenMod/cm-10.1

liboverlay : Update magnification limit for MDP 400