Nuvoton NPCM Peripheral Serial Peripheral Interface(PSPI) controller driver

Nuvoton NPCM7xx SOC support two PSPI channels.

Required properties:
 - compatible : "nuvoton,npcm750-pspi" for NPCM7XX BMC
 - #address-cells : should be 1. see spi-bus.txt
 - #size-cells : should be 0. see spi-bus.txt
 - specifies physical base address and size of the register.
 - interrupts : contain PSPI interrupt.
 - clocks : phandle of PSPI reference clock.
 - clock-names: Should be "clk_apb5".
 - pinctrl-names : a pinctrl state named "default" must be defined.
 - pinctrl-0 : phandle referencing pin configuration of the device.
 - cs-gpios: Specifies the gpio pins to be used for chipselects.
            See: Documentation/devicetree/bindings/spi/spi-bus.txt

Optional properties:
- clock-frequency : Input clock frequency to the PSPI block in Hz.
		    Default is 25000000 Hz.

Aliases:
- All the SPI controller nodes should be represented in the aliases node using
  the following format 'spi{n}' withe the correct numbered in "aliases" node.

Example:

aliases {
	spi0 = &spi0;
};

spi0: spi@f0200000 {
	compatible = "nuvoton,npcm750-pspi";
	reg = <0xf0200000 0x1000>;
	pinctrl-names = "default";
	pinctrl-0 = <&pspi1_pins>;
	#address-cells = <1>;
	#size-cells = <0>;
	interrupts = <GIC_SPI 31 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&clk NPCM7XX_CLK_APB5>;
	clock-names = "clk_apb5";
	cs-gpios = <&gpio6 11 GPIO_ACTIVE_LOW>;
};