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>

include/asm-generic/gpio.h

@@ -49,6 +49,7 @@ struct module;
 struct device_node;
 
 #ifdef CONFIG_PINCTRL
+
 /**
  * struct gpio_pin_range - pin range controlled by a gpio chip
  * @head: list for maintaining set of pin ranges, used internally
@@ -61,6 +62,11 @@ struct gpio_pin_range {
 	struct pinctrl_dev *pctldev;
 	struct pinctrl_gpio_range range;
 };
+
+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
 
 /**