Select texture target based on pixel format

Adreno is not optimized for GL_TEXTURE_EXTERNAL_OES, making GPU
utilization (and power), high with GL_TEXTURE_EXTERNAL_OES for
RGB formats.

Change texture target from GL_EXTERNAL_TEXTURE_OES to dynamically
select between GL_EXTERNAL_TEXTURE_OES, and GL_TEXTURE_2D based
on the pixel format.

This change is done to reduce the composition time for 8x55

Change-Id: I89ab1d60b23eef55442a9fd338b2a05b3304ce61

Conflicts:
	libs/gui/SurfaceTexture.cpp
	services/surfaceflinger/Layer.cpp