leds: allow led-drivers to use a variable range of brightness values

This patch allows drivers to override the default maximum brightness value
of 255.  We take care to preserve backwards-compatibility as much as
possible, so that user-space ABI doesn't change for existing drivers.
LED trigger code has also been updated to use the per-LED maximum.

Signed-off-by: Guennadi Liakhovetski <lg@denx.de>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

drivers/leds/leds.h

@@ -20,8 +20,8 @@
 static inline void led_set_brightness(struct led_classdev *led_cdev,
 					enum led_brightness value)
 {
-	if (value > LED_FULL)
-		value = LED_FULL;
+	if (value > led_cdev->max_brightness)
+		value = led_cdev->max_brightness;
 	led_cdev->brightness = value;
 	if (!(led_cdev->flags & LED_SUSPENDED))
 		led_cdev->brightness_set(led_cdev, value);