dt-bindings: pinctrl: Add Nuvoton WPCM450

dt-bindings: pinctrl: Add Nuvoton WPCM450

This binding is heavily based on the one for NPCM7xx, because the
hardware is similar. There are some notable differences, however:

- The addresses of GPIO banks are not physical addresses but simple
  indices (0 to 7), because the GPIO registers are not laid out in
  convenient blocks.
- Pinmux settings can explicitly specify that the GPIO mode is used.

Certain pins support blink patterns in hardware. This is currently not
modelled in the DT binding.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220129115228.2257310-5-j.neuschaefer@gmx.net
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>