dt-bindings: pinctrl: ocelot: Add ServalT SoC support

Add the documentation for the Microsemi ServalT pinmuxing and gpio
controller.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Link: https://lore.kernel.org/r/20220125131858.309237-2-horatiu.vultur@microchip.com


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