Staging: xgifb: Remove all the references to XGIfb_accel

xgifb framebuffer driver has an option to use an accelerator engine that never
get used (XGIfb_accel is always 0).

An earlier patchset remove the code that depends on the accelerator being
activated. This patch removes all the references to XGIfb_accel.

Signed-off-by: Javier Martinez Canillas <martinez.javier@gmail.com>
Acked-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>