Avoids waiting for VBLANKS that never arrive on headless or otherwise
unconventional set-ups. Strategy taken from MEMX.
Signed-off-by: NRoy Spliet <rspliet@eclipso.eu>
Tested-by: NPierre Moreau <pierre.morrow@free.fr>
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>