staging: xgifb: move pseudo_palette into xgifb_video_info

pseudo_palette should be dynamically allocated for each fb.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>