gpiolib: fix up function prototypes etc

Commit 69e1601bca88809dc118abd1becb02c15a02ec71
"gpiolib: provide provision to register pin ranges"

Got most of it's function prototypes wrong, so fix this up by:

- Moving the void declarations into static inlines in
  <linux/gpio.h> (previously the actual prototypes were declared
  here...)

- Declare the gpiochip_add_pin_range() and
  gpiochip_remove_pin_ranges() functions in <asm-generic/gpio.h>
  together with the pin range struct declaration itself.

- Actually only implement these very functions in gpiolib.c
  if CONFIG_PINCTRL is set.

- Additionally export the symbols since modules will need to
  be able to do this.

Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -1185,6 +1185,7 @@ struct gpio_chip *gpiochip_find(void *data,
 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)
 {
@@ -1206,6 +1207,7 @@ void gpiochip_add_pin_range(struct gpio_chip *chip, const char *pinctl_name,
 
 	list_add_tail(&pin_range->node, &chip->pin_ranges);
 }
+EXPORT_SYMBOL_GPL(gpiochip_add_pin_range);
 
 void gpiochip_remove_pin_ranges(struct gpio_chip *chip)
 {
@@ -1217,11 +1219,9 @@ void gpiochip_remove_pin_ranges(struct gpio_chip *chip)
 				&pin_range->range);
 	}
 }
-#else
-void gpiochip_add_pin_range(struct gpio_chip *chip, const char *pinctl_name,
-		unsigned int pin_base, unsigned int npins) {}
-void gpiochip_remove_pin_ranges(struct gpio_chip *chip) {}
-#endif
+EXPORT_SYMBOL_GPL(gpiochip_remove_pin_ranges);
+
+#endif /* CONFIG_PINCTRL */
 
 /* These "optional" allocation calls help prevent drivers from stomping
  * on each other, and help provide better diagnostics in debugfs.