libgui: Add pre-MR2-compatible symbol for setPosition

SurfaceControl::setPosition now takes floats instead of integers as
arguments, which breaks linkability from pre-MR2 blobs. Add a direct
compatibility wrapper, since the values are treated in the same
way.

Change-Id: I0fd0708faeb4495a2dbbb659997d6500f165ec98
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_EGL_NEEDS_LEGACY_FB board flag
and requires the ro.bq.gpu_to_cpu_unsupported property set to 1
in order to work

Change-Id: I7db955e2cdd120018e349c14290e975788e70ed3