dt-bindings: gpio: Convert STMPE GPIO to YAML schema

This rewrites the STMPE GPIO bindings to a YAML schema.

We add the properties that are used in the widely used
STMPE GPIO device nodes found in the wild, most notably
interrupt support, so interrupt-cells and
interrupt-controller is now part of the bindings.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>