pinctrl: npcx: add pinctrl support for psl pads

This CL introduces how to configure PSL (Power Switch Logic) pads
properties such as input detection mode/polarity, pin-muxing and so
on via pinctrl mechanism. It includes:

1. Add two pinctrl properties and their enums for PSL input
   detection configuration.
    psl-in-mode:
      - "level"
      - "mode"
    psl-in-pole:
      - "low-falling"
      - "high-rising"

2. Add macro functions to get PSL input detection and pin-muxing
   configurations from 'pinmux', 'psl-offset' abd 'psl-polarity'
   properties.

Here is an example to configure PSL_IN2 as the PSL detection input and
its mode and polarity.

/* A falling edge detection type for PSL_IN2 */
&psl_in2_gp00 {
	psl-in-mode = "edge";
	psl-in-pol = "low-falling";
};

A device will be introduced later which uses this pinctrl node to
configure PSL input detection settings and how to turn off VCC1 power
rail by PSL_OUT.

Signed-off-by: Mulin Chao <mlchao@nuvoton.com>