pinctrl: nuvoton: Add driver for WPCM450

pinctrl: nuvoton: Add driver for WPCM450

This driver is based on the one for NPCM7xx, because the WPCM450 is a
predecessor of those SoCs. Notable differences:

- On WPCM450, the GPIO registers are not organized in multiple banks,
  but rather placed continually into the same register block. This
  affects how register offsets are computed.
- Pinmux nodes can explicitly select GPIO mode, whereas in the npcm7xx
  driver, this happens automatically when a GPIO is requested.

Some functionality implemented in the hardware was (for now) left unused
in the driver, specifically blinking and pull-up/down.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20220129115228.2257310-6-j.neuschaefer@gmx.net
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>