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
Merge commit 'refs/changes/02/79102/1' of http://review.cyanogenmod.org/CyanogenMod/android_frameworks_native into cm-12.0