frameworks/native: fix copy back dirty region

Copyback dirty region logic does copyback,
even when its not necessary causing 2ms delay.
Fix the logic to copy back only what is necessary.

Change-Id: I52de68258ac9f87d704ee5401f93417805fa6773
libgui: Bring back support for mHeap-based screenshots

Older graphics libraries throw a hissy fit when trying to lock
buffers for Surface-based screenshots, on at least Tegra2/3 and
Exynos4 hardware.

This patch depends on the BOARD_USE_MHEAP_SCREENSHOT board flag
and requires the ro.bq.gpu_to_cpu_unsupported property set to 1
in order to work.

Change-Id: I7db955e2cdd120018e349c14290e975788e70ed3