hwc: Enable downscale feature through system property

Add support to turn the MDP downscale feature ON through the
use of a system property. 'sys.hwc.mdp_downscale_enabled' shall be
set to 'true' in build.prop file to enable this functionality.

This is required for OEMs that might have privacy concerns over panel
size information being exposed.

Change-Id: I354b25b1fdabe5786aed7552f2afccda35412467
4 files changed