gpio: Support GPIO controllers without pin-ranges

Wake gpiochip_generic_request() call into the pinctrl helpers only if a
GPIO controller had any pin-ranges assigned to it. This allows a driver
to unconditionally use this helper if it supports multiple devices of
which only a subset have pin-ranges assigned to them.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20200319122737.3063291-2-thierry.reding@gmail.com
Tested-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -2745,7 +2745,10 @@ static inline void gpiochip_irqchip_free_valid_mask(struct gpio_chip *gpiochip)
  */
 int gpiochip_generic_request(struct gpio_chip *chip, unsigned offset)
 {
-	return pinctrl_gpio_request(chip->gpiodev->base + offset);
+	if (!list_empty(&chip->gpiodev->pin_ranges))
+		return pinctrl_gpio_request(chip->gpiodev->base + offset);
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(gpiochip_generic_request);