mmc: sdhci-of-esdhc: temporary fixup for eMMC HS400 issue

Currently only LX2160A eSDHC supports eMMC HS400. According to
a large number of tests, eMMC HS400 failed to work at 150MHz,
and for a few boards failed to work at 175MHz. But eMMC HS400
worked fine on 200MHz. We hadn't found the root cause but
setting eSDHC_DLLCFG0[DLL_FREQ_SEL] = 0 using slow delay chain
seemed to resovle this issue. Let's use this as fixup for now.

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