Prefer 16bpp surface formats

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

(Original author: Grigori Goronzy <greg@blackbox>)

Change-Id: Ia5aa00b9fcb197d25f7107a569103389a0337eb3

Conflicts:
	services/surfaceflinger/SurfaceFlinger.cpp
	services/surfaceflinger/SurfaceFlinger.h