fbdev: omapfb: Remove some deadcode

commit f76ee892 ("omapfb: copy omapdss & displays for omapfb")
took a copy of the omapdrm code into omapfb, however at that point
a couple of functions were already unused at that point.

Remove dispc_mgr_get_clock_div() and dispc_enable_fifomerge() from
the omapfb copy.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Helge Deller <deller@gmx.de>