dt-bindings: pinctrl: Add binding for BCM4908 pinctrl

It's hardware block that is part of every SoC from BCM4908 family.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220124102243.14912-1-zajec5@gmail.com


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