SurfaceFlinger: use HAS_CONTEXT_PRIORITY

The OMAP3 SGX530 EGL driver has this extension, and it appears to help
performance, so use it.

Change-Id: I5019674a3199e1efa69ccf57c8f860abdab645f9
Disable scissor optimization in the display stack

XXX: The scissor optimization is known to slow down SGX540; verify that
it slows down SGX530 as well

Change-Id: Ie1873456e755a745dbdffee941ece62eaacbca27
Add <linux/omapfb.h> header needed for hwcomposer
Enable building of hwcomposer.omap3
Build audio HAL components from source instead of using prebuilts