tools/leds: Add led_hw_brightness_mon program

LED subsystem supports POLLPRI on "brightness_hw_changed" sysfs file
of LED class devices. This tool demonstrates how to use the feature.

Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Pavel Machek <pavel@ucw.cz>

tools/leds/Makefile

@@ -3,11 +3,11 @@
 CC = $(CROSS_COMPILE)gcc
 CFLAGS = -Wall -Wextra -g -I../../include/uapi
 
-all: uledmon
+all: uledmon led_hw_brightness_mon
 %: %.c
 	$(CC) $(CFLAGS) -o $@ $^
 
 clean:
-	$(RM) uledmon
+	$(RM) uledmon led_hw_brightness_mon
 
 .PHONY: all clean