gpiolib: Introduce for_each_requested_gpio_in_range() macro

Introduce for_each_requested_gpio_in_range() macro which helps
to iterate over requested GPIO in a range. There are already
potential users of it, which are going to be converted
by the following patches.

For most of them for_each_requested_gpio() shortcut has been added.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200615150545.87964-2-andriy.shevchenko@linux.intel.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/gpio/driver.h

@@ -474,6 +474,22 @@ struct gpio_chip {
 extern const char *gpiochip_is_requested(struct gpio_chip *gc,
 			unsigned int offset);
 
+/**
+ * for_each_requested_gpio_in_range - iterates over requested GPIOs in a given range
+ * @chip:	the chip to query
+ * @i:		loop variable
+ * @base:	first GPIO in the range
+ * @size:	amount of GPIOs to check starting from @base
+ * @label:	label of current GPIO
+ */
+#define for_each_requested_gpio_in_range(chip, i, base, size, label)			\
+	for (i = 0; i < size; i++)							\
+		if ((label = gpiochip_is_requested(chip, base + i)) == NULL) {} else
+
+/* Iterates over all requested GPIO of the given @chip */
+#define for_each_requested_gpio(chip, i, label)						\
+	for_each_requested_gpio_in_range(chip, i, 0, chip->ngpio, label)
+
 /* add/remove chips */
 extern int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 				      struct lock_class_key *lock_key,