dt-bindings: pinctrl: convert Broadcom Northstar to the json-schema

dt-bindings: pinctrl: convert Broadcom Northstar to the json-schema

Important: this change converts the binding as it is. It includes
dependency on undocumented CRU that must be refactored. CRU must get
documented and offset property has to be reworked.

Above can (and will be) be handled once every CRU MFD subdevice gets
documented properly (including the pinmux).

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210421182041.22636-1-zajec5@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>