pinctrl/rockchip: add a queue for deferred pin output settings on probe

pinctrl/rockchip: add a queue for deferred pin output settings on probe

The separation of pinctrl and gpio drivers created a tiny window where
a pinconfig setting might produce a null-pointer dereference.

The affected device were rk3288-veyron devices in this case.

Pinctrl-hogs are claimed when the pinctrl driver is registered,
at which point their pinconfig settings will be applied.
At this time the now separate gpio devices will not have been created
yet and the matching driver won't have probed yet, making the gpio->foo()
call run into a null-ptr.

As probing is not really guaranteed to have been completed at a specific
time, introduce a queue that can hold the output settings until the gpio
driver has probed and will (in a separate patch) fetch the elements
of the list.

We expect the gpio driver to empty the list, but will nevertheless empty
it ourself on remove if that didn't happen.

Fixes: 9ce9a02039de ("pinctrl/rockchip: drop the gpio related codes")
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20210913224926.1260726-4-heiko@sntech.de
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>