gpio: tps65086: Add DT bindings for the TPS65086 GPO controller

The TPS65086 PMIC contains several regulators and a GPO controller.
Add bindings for the TPS65086 GPO controller.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>