MFC r349428,r349433: owc_gpiobus: clean / fix up the driver module things
"fdt" is removed from the driver module name as the driver does not
require FDT and can work very well on hints based systems.
A module dependency is added for gpiobus. Without that owc cannot
resolve symbols in gpiobus if both are loaded as kernel modules.
Finally, a driver module module version is added.