dt-bindings: gpio-mmio: Add ngpios property

This adds the ngpios property to MMIO GPIO. We restrict the
property to 1..63 since there is no point in 0 GPIO lines and
we support up to 64bits wide registers for now.

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20241017-gpio-ngpios-v2-1-cecfdb38d40e@linaro.org


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>