staging: xgifb: vb_setmode: make XGI_SetXG21FPBits() static

XGI_SetXG21FPBits() can be made static. Move the function, so that
forward declaration is not needed.

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