hwc: send layer with non-contiguous buffers to GPU

when layer containing non-contiguous buffers are send to MDP,
flickers are observed

Conflicts:
	libhwcomposer/hwc_mdpcomp.cpp

CRs-Fixed: 624456
Change-Id: I4bcea959bd4849028368316aae39d1b0b17fa5b3
hwc: Do not use C2D composition for plane alpha

When C2D is used for plane alpha and immediately falls to GPU
   results in flicker for difference in composition

Change-Id: I2ae43c6ed22c829e952a0a4edee7f83c24645172