OMAPDSS: DISPC: Remove Fake VSYNC support

Fake VSYNC support is a hack and has some bugs in it. It isn't used by any user
of DSS. Remove Fake VSYNC support. For DSI command mode and RFBI panels, a user
of DSS should wait for the completion of a frame by using the panel driver's
sync op.

Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>