Lantiq XWAY pinmux controller

Required properties:
- compatible: "lantiq,pinctrl-xway" or "lantiq,pinctrl-xr9"
- reg: Should contain the physical address and length of the gpio/pinmux
  register range

Please refer to pinctrl-bindings.txt in this directory for details of the
common pinctrl bindings used by client devices, including the meaning of the
phrase "pin configuration node".

Lantiq's pin configuration nodes act as a container for an abitrary number of
subnodes. Each of these subnodes represents some desired configuration for a
pin, a group, or a list of pins or groups. This configuration can include the
mux function to select on those group(s), and two pin configuration parameters:
pull-up and open-drain

The name of each subnode is not important as long as it is unique; all subnodes
should be enumerated and processed purely based on their content.

Each subnode only affects those parameters that are explicitly listed. In
other words, a subnode that lists a mux function but no pin configuration
parameters implies no information about any pin configuration parameters.
Similarly, a pin subnode that describes a pullup parameter implies no
information about e.g. the mux function.

We support 2 types of nodes.

Definition of mux function groups:

Required subnode-properties:
- lantiq,groups : An array of strings. Each string contains the name of a group.
  Valid values for these names are listed below.
- lantiq,function: A string containing the name of the function to mux to the
  group. Valid values for function names are listed below.

Valid values for group and function names:

  mux groups:
    exin0, exin1, exin2, jtag, ebu a23, ebu a24, ebu a25, ebu clk, ebu cs1,
    ebu wait, nand ale, nand cs1, nand cle, spi, spi_cs1, spi_cs2, spi_cs3,
    spi_cs4, spi_cs5, spi_cs6, asc0, asc0 cts rts, stp, nmi , gpt1, gpt2,
    gpt3, clkout0, clkout1, clkout2, clkout3, gnt1, gnt2, gnt3, req1, req2,
    req3

  additional mux groups (XR9 only):
    mdio, nand rdy, nand rd, exin3, exin4, gnt4, req4

  functions:
    spi, asc, cgu, jtag, exin, stp, gpt, nmi, pci, ebu, mdio


Definition of pin configurations:

Required subnode-properties:
- lantiq,pins : An array of strings. Each string contains the name of a pin.
  Valid values for these names are listed below.

Optional subnode-properties:
- lantiq,pull: Integer, representing the pull-down/up to apply to the pin.
    0: none, 1: down, 2: up.
- lantiq,open-drain: Boolean, enables open-drain on the defined pin.

Valid values for XWAY pin names:
  Pinconf pins can be referenced via the names io0-io31.

Valid values for XR9 pin names:
  Pinconf pins can be referenced via the names io0-io55.

Example:
	gpio: pinmux@E100B10 {
		compatible = "lantiq,pinctrl-xway";
		pinctrl-names = "default";
		pinctrl-0 = <&state_default>;

		#gpio-cells = <2>;
		gpio-controller;
		reg = <0xE100B10 0xA0>;

		state_default: pinmux {
			stp {
				lantiq,groups = "stp";
				lantiq,function = "stp";
			};
			pci {
				lantiq,groups = "gnt1";
				lantiq,function = "pci";
			};
			conf_out {
				lantiq,pins = "io4", "io5", "io6"; /* stp */
				lantiq,open-drain;
				lantiq,pull = <0>;
			};
		};
	};