mmc: sdhci-esdhc-imx: Fix DAT line software reset

On i.MX25, the eSDHC DAT line software reset (SYSCTL.RSTD) unexpectedly
clears at least the data transfer width (PROCTL.DTW), which then results
in data CRC errors. This behavior is not documented, but it has actually
been observed. Consequently, the DAT line software resets triggered by
sdhci.c in case of errors caused unrecoverable errors.

Fix this by making sure that the DAT line software reset does not alter
the Host Control register. This behavior being undocumented, it may also
be present on other i.MX SoCs, so apply this fix for the whole i.MX
family.

Signed-off-by: Benoît Thébaudeau <benoit@wsystem.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>