backlight: lp855x_bl: support new LP8555 device

LP8555 is one of the LP855x family devices.

This device needs pre_init_device() and post_init_device() driver
structure.  It's same as LP8557, so the device configuration code is
shared with LP8557.  Backlight outputs are generated from dual DC-DC boost
converters.  It's configurable EPROM settings which are defined in the
platform data.

Driver documentation and device tree bindings are updated.

Signed-off-by: Milo Kim <milo.kim@ti.com>
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index d4a7a35..a65dd06 100644
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -388,8 +388,8 @@
 	tristate "Backlight driver for TI LP855X"
 	depends on BACKLIGHT_CLASS_DEVICE && I2C
 	help
-	  This supports TI LP8550, LP8551, LP8552, LP8553, LP8556 and LP8557
-	  backlight driver.
+	  This supports TI LP8550, LP8551, LP8552, LP8553, LP8555, LP8556 and
+	  LP8557 backlight driver.
 
 config BACKLIGHT_LP8788
 	tristate "Backlight driver for TI LP8788 MFD"