gpiolib: define GPIOD_FLAG_SHARED

Define a new GPIO descriptor flag for marking pins that are shared by
multiple consumer. This flag will be used in several places so we need
to do it in advance and separately from other changes.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20251112-gpio-shared-v4-2-b51f97b1abd8@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Author: Bartosz Golaszewski

drivers/gpio/gpiolib.h

@@ -204,6 +204,7 @@ struct gpio_desc {
 #define GPIOD_FLAG_EDGE_FALLING		17 /* GPIO CDEV detects falling edge events */
 #define GPIOD_FLAG_EVENT_CLOCK_REALTIME	18 /* GPIO CDEV reports REALTIME timestamps in events */
 #define GPIOD_FLAG_EVENT_CLOCK_HTE	19 /* GPIO CDEV reports hardware timestamps in events */
+#define GPIOD_FLAG_SHARED		20 /* GPIO is shared by multiple consumers */
 
 	/* Connection label */
 	struct gpio_desc_label __rcu *label;