gpiolib: separation of pin concerns

The fact that of_gpiochip_add_pin_range() and
gpiochip_add_pin_range() share too much code is fragile and
will invariably mean that bugs need to be fixed in two places
instead of one.

So separate the concerns of gpiolib.c and gpiolib-of.c and
have the latter call the former as back-end. This is necessary
also when going forward with other device descriptions such
as ACPI.

This is done by:

- Adding a return code to gpiochip_add_pin_range() so we can
  reliably check whether this succeeds.

- Get rid of the custom of_pinctrl_add_gpio_range() from
  pinctrl. Instead create of_pinctrl_get() to just retrive the
  pin controller per se from an OF node. This composite
  function was just begging to be deleted, it was way to
  purpose-specific.

- Use pinctrl_dev_get_name() to get the name of the retrieved
  pin controller and use that to call back into the generic
  gpiochip_add_pin_range().

Now the pin range is only allocated and tied to a pin
controller from the core implementation in gpiolib.c.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -1187,8 +1187,8 @@ EXPORT_SYMBOL_GPL(gpiochip_find);
 
 #ifdef CONFIG_PINCTRL
 
-void gpiochip_add_pin_range(struct gpio_chip *chip, const char *pinctl_name,
-		unsigned int pin_base, unsigned int npins)
+int gpiochip_add_pin_range(struct gpio_chip *chip, const char *pinctl_name,
+			   unsigned int pin_base, unsigned int npins)
 {
 	struct gpio_pin_range *pin_range;
 
@@ -1196,7 +1196,7 @@ void gpiochip_add_pin_range(struct gpio_chip *chip, const char *pinctl_name,
 	if (!pin_range) {
 		pr_err("%s: GPIO chip: failed to allocate pin ranges\n",
 				chip->label);
-		return;
+		return -ENOMEM;
 	}
 
 	pin_range->range.name = chip->label;
@@ -1207,6 +1207,8 @@ void gpiochip_add_pin_range(struct gpio_chip *chip, const char *pinctl_name,
 			&pin_range->range);
 
 	list_add_tail(&pin_range->node, &chip->pin_ranges);
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(gpiochip_add_pin_range);