dt-bindings: pinctrl: mediatek: deprecate custom drive strength property

Deprecate mediatek,drive-strength-adv which shall not exist, that was an
unnecessary property that leaked upstream from downstream kernels and
there's no reason to use it.

The generic property drive-strength-microamp should be used instead.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Alexandre Mergnat <amergnat@baylibre.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230327-cleanup-pinctrl-binding-v3-1-6f56d5c7a8de@baylibre.com


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