display: Enable copybit on msm8610

This change is the hwc and copybit changes need to enable
composition to go through mdp on msm8610.

Change-Id: If0df3a247c5f4f4310966d14fe8fd839bf84b9d5
copybit: Fix type conversion error for GCC 4.7

    GCC 4.7 has stricter type conversion rules in copybit.cpp

Change-Id: I7f8572e2d9416ccb2ba17e707c7f75a2e69d69cf