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/pinctrl/devicetree.c

@@ -106,8 +106,7 @@ static struct pinctrl_dev *find_pinctrl_by_of_node(struct device_node *np)
 	return NULL;
 }
 
-struct pinctrl_dev *of_pinctrl_add_gpio_range(struct device_node *np,
-		struct pinctrl_gpio_range *range)
+struct pinctrl_dev *of_pinctrl_get(struct device_node *np)
 {
 	struct pinctrl_dev *pctldev;
 
@@ -115,7 +114,6 @@ struct pinctrl_dev *of_pinctrl_add_gpio_range(struct device_node *np,
 	if (!pctldev)
 		return NULL;
 
-	pinctrl_add_gpio_range(pctldev, range);
 	return pctldev;
 }