s3cfb: Notify userspace of vsync using sysfs, make uevents optional

Change-Id: I6fe8de47961d5c0ba73eb45543a675b6fd4344a4
i9300, n7100, n80xx: enable sysfs vsync notifications

Change-Id: Iba408423510aeaf8e27eff2490100978c0a9e757