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@xxxxxxxxxx>
Signed-off-by: Axe Yang <axe.yang@xxxxxxxxxxxx>