mmc: sdhci-esdhc-imx: enable hw auto retuning for MAN_TUNING

Indicating hw auto retuning support for mx6qdl in the fake caps_1
register and enable auto retuning in post_tuning process after
tuning completes.

Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>