Axis ARTPEC-6 Pin Controller

Required properties:
- compatible: "axis,artpec6-pinctrl".
- reg: Should contain the register physical address and length for the pin
       controller.

A pinctrl node should contain at least one subnode representing the pinctrl
groups available on the machine. Each subnode will list the mux function
required and what pin group it will use. Each subnode will also configure the
drive strength and bias pullup of the pin group. If either of these options is
not set, its actual value will be unspecified.


Required subnode-properties:
- function: Function to mux.
- groups: Name of the pin group to use for the function above.

	Available functions and groups (function: group0, group1...):
		gpio: cpuclkoutgrp0, udlclkoutgrp0, i2c1grp0, i2c2grp0,
		      i2c3grp0, i2s0grp0, i2s1grp0, i2srefclkgrp0, spi0grp0,
		      spi1grp0, pciedebuggrp0, uart0grp0, uart0grp1, uart1grp0,
		      uart2grp0, uart2grp1, uart3grp0, uart4grp0, uart5grp0
		cpuclkout: cpuclkoutgrp0
		udlclkout: udlclkoutgrp0
		i2c1: i2c1grp0
		i2c2: i2c2grp0
		i2c3: i2c3grp0
		i2s0: i2s0grp0
		i2s1: i2s1grp0
		i2srefclk: i2srefclkgrp0
		spi0: spi0grp0
		spi1: spi1grp0
		pciedebug: pciedebuggrp0
		uart0: uart0grp0, uart0grp1
		uart1: uart1grp0
		uart2: uart2grp0, uart2grp1
		uart3: uart3grp0
		uart4: uart4grp0
		uart5: uart5grp0
		nand: nandgrp0
		sdio0: sdio0grp0
		sdio1: sdio1grp0
		ethernet: ethernetgrp0


Optional subnode-properties (see pinctrl-bindings.txt):
- drive-strength: 4, 6, 8, 9 mA.  For SD and NAND pins, this is for 3.3V VCCQ3.
- bias-pull-up
- bias-disable

Examples:
pinctrl@f801d000 {
	compatible = "axis,artpec6-pinctrl";
	reg = <0xf801d000 0x400>;

	pinctrl_uart0: uart0grp {
		function = "uart0";
		groups = "uart0grp0";
		drive-strength = <4>;
		bias-pull-up;
	};
	pinctrl_uart3: uart3grp {
		function = "uart3";
		groups = "uart3grp0";
	};
};
uart0: uart@f8036000 {
	compatible = "arm,pl011", "arm,primecell";
	reg = <0xf8036000 0x1000>;
	interrupts = <0 104 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&pll2div24>, <&apb_pclk>;
	clock-names = "uart_clk", "apb_pclk";
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_uart0>;
};
uart3: uart@f8039000 {
	compatible = "arm,pl011", "arm,primecell";
	reg = <0xf8039000 0x1000>;
	interrupts = <0 128 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&pll2div24>, <&apb_pclk>;
	clock-names = "uart_clk", "apb_pclk";
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_uart3>;
};