dt-bindings: gpio: Binding for MStar MSC313 GPIO controller

Add a binding description for the MStar/SigmaStar GPIO controller
found in the MSC313 and later ARMv7 SoCs.

Signed-off-by: Daniel Palmer <daniel@0x0f.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201129110803.2461700-3-daniel@0x0f.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>