Since the GPIO jacks are only supported if gpiolib is built and fail to
compile otherwise add a build depedency.  This is unlikely to have any
practical impact outside of coverage testing.
Reported-by: NRussell King <linux@arm.linux.org.uk>
Signed-off-by: NMark Brown <broonie@linaro.org>
Acked-by: NJarkko Nikula <jarkko.nikula@bitmer.com>