pinctrl: probe pinctrl drivers during post-bind

Currently, pinctrl drivers only get probed if pinconf is actually being
used, however on SoC-s like Armada 3720 pinctrl driver is a also the GPIO
driver.

So, if the pinctrl driver doesn't get probed GPIO-s won't get registered
and thus they cannot be used.

This is a problem on the Methode eDPU as it just uses SB pins as GPIO-s
and without them being registered networking won't work as it only has
one SFP slot and the TX disable GPIO is on the SB controller.

So, probe the pinctrl drivers using DM_FLAG_PROBE_AFTER_BIND like LED
uclass does.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Reviewed-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>