OMAP: DSS2: OMAPFB: add support for FBIO_WAITFORVSYNC

FBIO_WAITFORVSYNC is a stardard ioctl for waiting vsync, already
used by some userspace, so add it as an alias for OMAPFB_WAITFORVSYNC.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>