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
hwc: hwc_sync - populate correct fences for BLIT

Previously, the acquire and release fences for BLIT
composition were populated using same logic as Overlay,
but BLIT composition consists of separate BLIT step
before screen refresh, and app buffers are no longer
required after BLIT. So holding the buffers for both
the steps is unnecessary and impacts performance.

This change adds condition for BLIT in fence population
logic in hwc_sync and populates the right fences for the
App Buffers and Display Refresh during BLIT composition.

Change-Id: I9998a7052c0375acb32a174bdf0469d2a88f79e8