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.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/mtk-sd.yaml

@@ -145,6 +145,15 @@ properties:
     minimum: 0
     maximum: 7
 
+  mediatek,tuning-step:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      Some SoCs need extend tuning step for better delay value to avoid CRC issue.
+      If not present, default tuning step is 32. For eMMC and SD, this can yield
+      satisfactory calibration results in most cases.
+    enum: [32, 64]
+    default: 32
+
   resets:
     maxItems: 1