pinctrl: rp1: Implement RaspberryPi RP1 gpio support

pinctrl: rp1: Implement RaspberryPi RP1 gpio support

The RP1 is an MFD supporting a gpio controller and /pinmux/pinctrl.
Add minimum support for the gpio only portion. The driver is in
pinctrl folder since upcoming patches will add the pinmux/pinctrl
support where the gpio part can be seen as an addition.

Signed-off-by: Andrea della Porta <andrea.porta@suse.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Stefan Wahren <wahrenst@gmx.net>
Link: https://lore.kernel.org/r/20250529135052.28398-5-andrea.porta@suse.com
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>