Documentation: leds: update LP55xx family devices

 Update changed platform data information.
 Add leds-lp55xx.txt which includes the firmware interface description.

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>
diff --git a/Documentation/leds/00-INDEX b/Documentation/leds/00-INDEX
index 5fefe37..5246090 100644
--- a/Documentation/leds/00-INDEX
+++ b/Documentation/leds/00-INDEX
@@ -6,5 +6,7 @@
 	- notes on how to use the leds-lp5521 driver.
 leds-lp5523.txt
 	- notes on how to use the leds-lp5523 driver.
+leds-lp55xx.txt
+	- description about lp55xx common driver.
 leds-lm3556.txt
 	- notes on how to use the leds-lm3556 driver.