Bring radeon up to speed with the async event synchronization for
drmWaitVblank. See c9a9c5e02aedc1a2815877b0268f886d2640b771 for
more information. Without this patch event never get delivered
to userspace client.
Signed-off-by: Jerome Glisse <jglisse@redhat.com> Signed-off-by: Dave Airlie <airlied@redhat.com>