dt-bindings: mfd: Add lm36274 bindings to ti-lmu

dt-bindings: mfd: Add lm36274 bindings to ti-lmu

Add the LM36274 backlight driver with regulator support.
This is a multi-function device for backlight applications.

Backlight properties will be documented in it's a supplemental
bindings document.

Regulator support is documented in the regulator/lm363x-regulator.txt

http://www.ti.com/lit/ds/symlink/lm36274.pdf

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