Prefer 16bpp surface formats

Adds a property to use RGB565 surface formats for the opaque
surface default, enabled by default.

Change-Id: Iac9bbc8292a863e2ab86093df3ecf218e4ec61e1
Revert "libgui: Use fences for all QCOM targets"

This reverts commit be1b7537097779385da94ae98e0cca76732d74ba.