leds: Add support for hardware accelerated LED flashing

Extends the leds subsystem with a blink_set() callback function which can
be optionally implemented by a LED driver. If implemented, the driver can use
the hardware acceleration for blinking a LED.

Signed-off-by: Márton Németh <nm127@freemail.hu>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index cf3a6d4..659448e 100644
--- a/drivers/leds/Kconfig
+++ b/drivers/leds/Kconfig
@@ -152,7 +152,11 @@
 	depends on LEDS_TRIGGERS
 	help
 	  This allows LEDs to be controlled by a programmable timer
-	  via sysfs. If unsure, say Y.
+	  via sysfs. Some LED hardware can be programmed to start
+	  blinking the LED without any further software interaction.
+	  For more details read Documentation/leds-class.txt.
+
+	  If unsure, say Y.
 
 config LEDS_TRIGGER_IDE_DISK
 	bool "LED IDE Disk Trigger"