staging: xgifb: enable forcecrt2type on XG21

Make "forcecrt2type" to apply also for XG21. The patch enables user to
switch LVDS LCD ON/OFF without the need to update the video BIOS.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>