staging/xgifb: Move register helper functions to header

and mark them as static inline.
This shrinks the compiled module from 137442 to 117732 bytes and we also
get rid of vb_util.c

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>