dt: bindings: lp50xx: Introduce the lp50xx family of RGB drivers

dt: bindings: lp50xx: Introduce the lp50xx family of RGB drivers

Introduce the bindings for the Texas Instruments LP5036, LP5030, LP5024,
LP5018, LP5012 and LP5009 RGB LED device driver.  The LP5036/30/24/18/12/9
can control RGB LEDs individually or as part of a control bank group.
These devices have the ability to adjust the mixing control for the RGB
LEDs to obtain different colors independent of the overall brightness of
the LED grouping.

Datasheet:
http://www.ti.com/lit/ds/symlink/lp5012.pdf
http://www.ti.com/lit/ds/symlink/lp5024.pdf
http://www.ti.com/lit/ds/symlink/lp5036.pdf

Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>