dt-bindings: mmc: mtk-sd: add tuning steps related property

dt-bindings: mmc: mtk-sd: add tuning steps related property

Add 'mediatek,tuning-steps' setting. This property will give MSDC
a chance to extend tuning steps up to 64. With more tuning steps,
MSDC may achieve a more optimal calibration result, thus avoiding
potential CRC issues.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Axe Yang <axe.yang@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20231207063535.29546-2-axe.yang@mediatek.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>