leds: lm36274: Introduce the TI LM36274 LED driver

Introduce the LM36274 LED driver.  This driver uses the ti-lmu
MFD driver to probe this LED driver.  The driver configures only the
LED registers and enables the outputs according to the config file.

The driver utilizes the TI LMU (Lighting Management Unit) LED common
framework to set the brightness bits.

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