mmc: sdhci-of-esdhc: workaround for unreliable pulse width detection

This was a SoC issue on LX2160A Rev1.0.
eSDHC_DLLCFG1[DLL_PD_PULSE_STRETCH_SEL] must be set to 0 to
get 4 delay cells in the pulse width detection logic for eMMC
HS400 mode. Otherwise it would cause unexpected HS400 issue.
This patch is to clear this bit always for affected SoC when
reset for all, since this bit doesn't affect other speed modes.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>