dt-bindings: power: Add BQ28z610 compatible

Add the Texas Instruments bq28z610 battery monitor to the bq27xxx
binding.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>