pinctrl: bcm: add bcm63xx base code

Add a helper for registering BCM63XX pin controllers.

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/20210324081923.20379-5-noltari@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>