dt: bindings: lm3601x: Introduce the lm3601x driver

Introduce the device tree bindings for the lm3601x
family of LED torch, flash and IR drivers.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>