gpio: sandbox: Add GPIOD_IS_AF for gpio configured in alternate function

This allows to test if a pin's label if displayed using gpio_get_status()
when this pin is configured in alternate function.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index 81f63f0..0fcf709 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -127,6 +127,7 @@
 #define GPIOD_OPEN_SOURCE	BIT(6)	/* GPIO is open source type */
 #define GPIOD_PULL_UP		BIT(7)	/* GPIO has pull-up enabled */
 #define GPIOD_PULL_DOWN		BIT(8)	/* GPIO has pull-down enabled */
+#define GPIOD_IS_AF		BIT(9)	/* GPIO is an alternate function */
 
 /* Flags for updating the above */
 #define GPIOD_MASK_DIR		(GPIOD_IS_OUT | GPIOD_IS_IN | \