pinctrl: ocelot: Extend support for lan966x

This patch extends pinctrl-ocelot driver to support also the
lan966x. Register layout is same as ocelot. It has 78 GPIOs.
Requires 3 registers ALT0, ALT1, ALT2 to configure ALT mode.
Signed-off-by: Kavyasree Kotagiri <kavyasree.kotagiri@microchip.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211118112548.14582-3-kavyasree.kotagiri@microchip.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>