mmc: sdhci-of-esdhc: fix eMMC couldn't work after kexec

The bit eSDHC_TBCTL[TB_EN] couldn't be reset by eSDHC_SYSCTL[RSTA] which is
used to reset for all. The driver should make sure it's cleared before card
initialization, otherwise the initialization would fail.

Signed-off-by: yinbo.zhu <yinbo.zhu@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>