Introduce the Texas Instruments LM3532 White LED driver.
The driver supports ALS configurability or manual brightness
control.

The driver also supports associating LED strings with specific
control banks in a group or as individually controlled strings.
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>