dt-bindings: gpio: Convert Broadcom STB GPIO to YAML

Convert the Broadcom STB GPIO Device Tree binding to YAML to help with
validation.

Acked-by: Gregory Fong <gregory.0xf0@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Bartosz Golaszewski <brgl@bgdev.pl>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20211208003727.3596577-6-f.fainelli@gmail.com


Signed-off-by: Rob Herring <robh@kernel.org>