Add BOARD_EGL_NEEDS_LEGACY_FB flags to SurfaceFlinger

To solve soft-reboot on Omni for p4wifi

Big thanks to Daniel Tjandra/AAccount

Change-Id: Id4a83ee3b636b0e2072497e74a37fc998dd85030
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

Conflicts:
	services/surfaceflinger/SurfaceFlinger.cpp