*ST pin controller.

Each multi-function pin is controlled, driven and routed through the
PIO multiplexing block. Each pin supports GPIO functionality (ALT0)
and multiple alternate functions(ALT1 - ALTx) that directly connect
the pin to different hardware blocks.

When a pin is in GPIO mode, Output Enable (OE), Open Drain(OD), and
Pull Up (PU) are driven by the related PIO block.

ST pinctrl driver controls PIO multiplexing block and also interacts with
gpio driver to configure a pin.

Required properties: (PIO multiplexing block)
- compatible	: should be "st,<SOC>-<pio-block>-pinctrl"
	like st,stih415-sbc-pinctrl, st,stih415-front-pinctrl and so on.
- gpio-controller : Indicates this device is a GPIO controller
- #gpio-cells	  : Should be one. The first cell is the pin number.
- st,retime-pin-mask	: Should be mask to specify which pins can be retimed.
	If the property is not present, it is assumed that all the pins in the
	bank are capable of retiming. Retiming is mainly used to improve the
	IO timing margins of external synchronous interfaces.
- st,bank-name		: Should be a name string for this bank as
			specified in datasheet.
- st,syscfg		: Should be a phandle of the syscfg node.

Example:
	pin-controller-sbc {
		#address-cells	= <1>;
		#size-cells	= <1>;
		compatible	= "st,stih415-sbc-pinctrl";
		st,syscfg	= <&syscfg_sbc>;
		ranges 		= <0 0xfe610000 0x5000>;
		PIO0: gpio@fe610000 {
			gpio-controller;
			#gpio-cells	= <1>;
			reg		= <0 0x100>;
			st,bank-name	= "PIO0";
		};
		...
		pin-functions nodes follow...
	};


Contents of function subnode node:
----------------------
Required properties for pin configuration node:
- st,pins	: Child node with list of pins with configuration.

Below is the format of how each pin conf should look like.

<bank offset mux mode rt_type rt_delay rt_clk>

Every PIO is represented with 4-7 parameters depending on retime configuration.
Each parameter is explained as below.

-bank		: Should be bank phandle to which this PIO belongs.
-offset		: Offset in the PIO bank.
-mux		: Should be alternate function number associated this pin.
		Use same numbers from datasheet.
-mode		:pin configuration is selected from one of the below values.
		IN
		IN_PU
		OUT
		BIDIR
		BIDIR_PU

-rt_type	Retiming Configuration for the pin.
		Possible retime configuration are:

		-------		-------------
		value		args
		-------		-------------
		NICLK		<delay> <clk>
		ICLK_IO		<delay> <clk>
		BYPASS		<delay>
		DE_IO		<delay> <clk>
		SE_ICLK_IO	<delay> <clk>
		SE_NICLK_IO	<delay> <clk>

- delay	is retime delay in pico seconds as mentioned in data sheet.

- rt_clk	:clk to be use for retime.
		Possible values are:
		CLK_A
		CLK_B
		CLK_C
		CLK_D

Example of mmcclk pin which is a bi-direction pull pu with retime config
as non inverted clock retimed with CLK_B and delay of 0 pico seconds:

pin-controller {
	...
	mmc0 {
		pinctrl_mmc: mmc {
			st,pins {
				mmcclk = <&PIO13 4 ALT4 BIDIR_PU NICLK 0 CLK_B>;
				...
			};
		};
	...
	};
};

sdhci0:sdhci@fe810000{
	...
	pinctrl-names = "default";
	pinctrl-0	= <&pinctrl_mmc>;
};