pinctrl: update GPIO range doc

 - GPIO range : [48 .. 55]

 - pin range  : [64 .. 71]

The above examples assume the mapping between the GPIOs and pins is

linear. If the mapping is sparse or haphazard, an array of arbitrary pin

numbers can be encoded in the range like this:

static const unsigned range_pins[] = { 14, 1, 22, 17, 10, 8, 6, 2 };

static struct pinctrl_gpio_range gpio_range = {

	.name = "chip",

	.id = 0,

	.base = 32,

	.pins = &range_pins,

	.npins = ARRAY_SIZE(range_pins),

	.gc = &chip;

};

In this case the pin_base property will be ignored.

When GPIO-specific functions in the pin control subsystem are called, these

ranges will be used to look up the appropriate pin controller by inspecting

and matching the pin to the pin ranges across all controllers. When a

will be called on that specific pin controller.

For all functionalities dealing with pin biasing, pin muxing etc, the pin

controller subsystem will subtract the range's .base offset from the passed

in gpio number, and add the ranges's .pin_base offset to retrive a pin number.

After that, the subsystem passes it on to the pin control driver, so the driver

controller subsystem will look up the corresponding pin number from the passed

in gpio number, and use the range's internals to retrive a pin number. After

that, the subsystem passes it on to the pin control driver, so the driver

will get an pin number into its handled number range. Further it is also passed

the range ID value, so that the pin controller knows which range it should

deal with.

section 2.1 of Documentation/devicetree/bindings/gpio/gpio.txt on how to bind

pinctrl and gpio drivers.

PINMUX interfaces

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