egl: hwcomposer: handle acquire and release fences when locking/unlocking front buffer

In order to interact correctly with hwcomposer implementations >= 1.1 we have to handle
acquire and release fences correctly when locking or unlocking the front buffer.

Signed-off-by: Simon Busch <morphis@gravedo.de>
egl: hwcomposer: don't abort the application when expected front buffer state isn't available

Instead of aborting the running application hardly we should handle this more gracefully.

Signed-off-by: Simon Busch <morphis@gravedo.de>