dt: lm3532: Add lm3532 dt doc and update ti_lmu doc

Add the lm3532 device tree documentation.
Remove lm3532 device tree reference from the ti_lmu devicetree
documentation.

With the addition of the dedicated lm3532 documentation the device
can be removed from the ti_lmu.txt.

The reason for this is that the lm3532 dt documentation now defines
the ability to control LED output strings against different control
banks or groups multiple strings to be controlled by a single control
bank.

Another addition was for ALS lighting control and configuration.  The
LM3532 has a feature that can take in the ALS reading from 2 separate
ALS devices and adjust the brightness on the strings that are configured
to support this feature.

Finally the device specific properties were moved to the parent node
as these properties are not control bank configurable.  These include
the runtime ramp and the ALS configuration.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-for-MFD-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>