mmc: sdhci-esdhc-imx: explicitly reset tuning circuit via RSTT bit

mmc: sdhci-esdhc-imx: explicitly reset tuning circuit via RSTT bit

According to the i.MX Reference Manual, the RSTT bit (SYS_CTRL[28]) is
designed to reset the tuning circuit. While the Reference Manual states
that clearing EXECUTE_TUNING bit from 1 to 0 in AUTOCMD12_ERR_STATUS
can also set RSTT, this mechanism only works when the original
EXECUTE_TUNING bit was 1. When the bit is already 0, the tuning circuit
reset will not be triggered.

This explicit reset approach strengthens the tuning reliability and
aligns with the Reference Manual recommendations.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Signed-off-by: Luke Wang <ziniu.wang_1@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20250409075550.3413032-2-ziniu.wang_1@nxp.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>