Lantiq FALCON pinmux controller

Required properties:
- compatible: "lantiq,pinctrl-falcon"
- 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:
    por, ntr, ntr8k, hrst, mdio, bootled, asc0, spi, spi cs0, spi cs1, i2c,
    jtag, slic, pcm, asc1

  functions:
    rst, ntr, mdio, led, asc, spi, i2c, jtag, slic, pcm


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
- lantiq,drive-current: Boolean, enables drive-current
- lantiq,slew-rate: Boolean, enables slew-rate

Example:
	pinmux0 {
		compatible = "lantiq,pinctrl-falcon";
		pinctrl-names = "default";
		pinctrl-0 = <&state_default>;

		state_default: pinmux {
			asc0 {
				lantiq,groups = "asc0";
				lantiq,function = "asc";
			};
			ntr {
				lantiq,groups = "ntr8k";
				lantiq,function = "ntr";
			};
			i2c {
				lantiq,groups = "i2c";
				lantiq,function = "i2c";
			};
			hrst {
				lantiq,groups = "hrst";
				lantiq,function = "rst";
			};
		};
	};