The PIO2 driver errors when GPIOLIB, on which it depends, is not enabled.

Add dependancy when selecting the PIO2.
Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Martyn Welch <martyn.welch@ge.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>