reduce PB size from 2MB to 512KB

this allows us to enable h/w acceleration on low-end
devices while keeping memory usage down.

Bug: 6557760
Change-Id: I8af2de3038dc2579360b8b73aa452cb7a0e506a9
egl: Add support for BGRA_8888 format

* Select with BOARD_USE_BGRA_8888 flag

Change-Id: I79a5a9edfef9c264eeeb9807797d03208f9bdbd7