pinctrl: add a pincontrol driver for BCM6368

Add a pincontrol driver for BCM6368. BCM6368 allows muxing the first 32
GPIOs onto alternative functions. Not all are documented.

Co-developed-by: Jonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Link: https://lore.kernel.org/r/20210324081923.20379-17-noltari@gmail.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>