gpio: tps65086: Add GPO driver for the TPS65086 PMIC

Add support for the TPS65086 PMIC GPOs.

TPS65086 has four configurable GPOs that can be used for several
purposes. These are output only.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>