[media] lm3646: add new dual LED Flash driver

This patch adds the driver for the LM3646, dual LED Flash driver.
The LM3646 has two 1.5A sync. boost converter with dual white current source.
It is controlled via an I2C compatible interface.
Each flash brightness, torch brightness and enable/disable can be controlled.
Under voltage, input voltage monitor and thermal threshhold Faults are added.
Please refer the datasheet http://www.ti.com/lit/ds/snvs962/snvs962.pdf

Signed-off-by: Daniel Jeong <gshark.jeong@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>