staging: xgifb: delete "off" option handling

It's possible to disable the built-in xgifb driver with the kernel
command line option:

	video=xgifb:off

This is already handled by the generic framebuffer layer (fb_get_options()
will return TRUE resulting in init failure), so no need to process the
option in the driver.

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