lxfb: set the H- and V-SYNC polarity of the flatpanel output

Fixup for the flatpanel output.  The geode_modedb attribute flags are used
to set the SYNC polarity of the flatpanel.  Without this patch our
flatpanel registers stayed unconfigured, so we just saw garbage output.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Cc: Andres Salomon <dilinger@collabora.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>