Before the split of gpio and pinctrl sections in their own driver,
rockchip_set_mux was called in pinmux_ops.gpio_set_direction for
configuring a pin in its GPIO function.

This is essential for cases where pinctrl is "bypassed" by gpio
consumers otherwise the GPIO function is not configured for the pin and
it does not work. Such was the case for the sysfs/libgpiod userspace
GPIO handling.

Let's re-implement the pinmux_ops.gpio_set_direction callback so that
the gpio subsystem can request from the pinctrl driver to put the pin in
its GPIO function.

Fixes: 9ce9a020 ("pinctrl/rockchip: drop the gpio related codes")
Cc: stable@vger.kernel.org
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Link: https://lore.kernel.org/r/20220930132033.4003377-2-foss+kernel@0leil.netSigned-off-by: Linus Walleij <linus.walleij@linaro.org>