dt-bindings: pinctrl: imx93: Add pinctrl binding

Add pinctrl binding doc for i.MX93

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220228010103.2725893-1-peng.fan@oss.nxp.com


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