gpio_led: add support for inverted polarity

Some GPIO connected LEDs have inverted polarity.
Introduce new config option: CONFIG_GPIO_LED_INVERTED_TABLE for the
specifying the inverted GPIO LEDs list and add support for this in the
gpio_led driver.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
Tested-by: Ilya Ledvich <ilya@compulab.co.il>
diff --git a/README b/README
index 7b393b7..5def773 100644
--- a/README
+++ b/README
@@ -1971,6 +1971,13 @@
 		status LED backend implementation. Define CONFIG_GPIO_LED
 		to include the gpio_led driver in the U-Boot binary.
 
+		CONFIG_GPIO_LED_INVERTED_TABLE
+		Some GPIO connected LEDs may have inverted polarity in which
+		case the GPIO high value corresponds to LED off state and
+		GPIO low value corresponds to LED on state.
+		In such cases CONFIG_GPIO_LED_INVERTED_TABLE may be defined
+		with a list of GPIO LEDs that have inverted polarity.
+
 - CAN Support:	CONFIG_CAN_DRIVER
 
 		Defining CONFIG_CAN_DRIVER enables CAN driver support