reset: gpio: convert the driver to using the auxiliary bus

reset: gpio: convert the driver to using the auxiliary bus

As the reset-gpio devices are purely virtual and never instantiated from
real firmware nodes, let's convert the driver to using the - more
fitting - auxiliary bus.

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>