gpiolib: discourage gpiochip_add_pin[group]_range for DT pinctrls

This patch adds the stern warning to the kerneldoc text of both
gpiochip_add_pin[group]_range() functions in hope of detering
developers from ever using them in their DeviceTree-supported
pinctrl drivers in the future.

For anyone affected: Please refer to Section 2.1 of
Documentation/devicetree/bindings/gpio/gpio.txt on how to
bind pinctrl and gpio drivers via the "gpio-ranges" property.
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -2077,6 +2077,11 @@ EXPORT_SYMBOL_GPL(gpiochip_generic_config);
  * @pctldev: the pin controller to map to
  * @gpio_offset: the start offset in the current gpio_chip number space
  * @pin_group: name of the pin group inside the pin controller
+ *
+ * Calling this function directly from a DeviceTree-supported
+ * pinctrl driver is DEPRECATED. Please see Section 2.1 of
+ * Documentation/devicetree/bindings/gpio/gpio.txt on how to
+ * bind pinctrl and gpio drivers via the "gpio-ranges" property.
  */
 int gpiochip_add_pingroup_range(struct gpio_chip *chip,
 			struct pinctrl_dev *pctldev,
@@ -2130,6 +2135,11 @@ EXPORT_SYMBOL_GPL(gpiochip_add_pingroup_range);
  *
  * Returns:
  * 0 on success, or a negative error-code on failure.
+ *
+ * Calling this function directly from a DeviceTree-supported
+ * pinctrl driver is DEPRECATED. Please see Section 2.1 of
+ * Documentation/devicetree/bindings/gpio/gpio.txt on how to
+ * bind pinctrl and gpio drivers via the "gpio-ranges" property.
  */
 int gpiochip_add_pin_range(struct gpio_chip *chip, const char *pinctl_name,
 			   unsigned int gpio_offset, unsigned int pin_offset,