EmuGL: Deliver every frame to a callback

To enable multi-touch on a tethered device, allow a callback to be
registered with the OpenGL renderer. On every frame, the framebuffer
is read into system memory and provided to the callback, so it can be
mirrored to the device.

This change is co-dependent on Idae3b026d52ed8dd666cbcdc3f3af80175c90ad3
in external/qemu.

Change-Id: I03c49bc55ed9e66ffb59462333181f77e7e46035
5 files changed