dt-bindings: pinctrl: mediatek,mt8365-pinctrl: add drive strength property

dt-bindings: pinctrl: mediatek,mt8365-pinctrl: add drive strength property

This SoC is able to drive the following output current:
- 2 mA
- 4 mA
- 6 mA
- 8 mA
- 10 mA
- 12 mA
- 14 mA
- 16 mA

Then drive-strength property is set with enum to reflect its HW capability.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Alexandre Mergnat <amergnat@baylibre.com>
Link: https://lore.kernel.org/r/20230327-cleanup-pinctrl-binding-v3-3-6f56d5c7a8de@baylibre.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>