dt-bindings: pinctrl: realtek: add RTD1315E pinctrl binding

Add device tree bindings for RTD1315E.

Signed-off-by: Tzuyi Chang <tychang@realtek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230919101117.4097-6-tychang@realtek.com


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