HWC/copybit : Add support for isFG in copybit

Some applications are sending the RGBA layer with constact alpha
0xFF and isOpaque=1. For these types of layer we are not getting
any wormHole regions.Hence we are seeing the previous content (framebuffer)
due to wrong selection of blending logic at kernel side.

For fixing these type of issues for MDP3 we are making Z order zero
layer as FG same as MDP4 to choose proper blending logic.

(cherry picked from commit 68a0f20dd31a753abdefd0be64287d93f03036cc)

Change-Id: Iad5f69bc411d22229aa509dc5bfb351744615049
CRs-fixed: 405802
CRs-fixed: 406503
CRs-fixed: 386356