mmc: sdhci-esdhc-imx: add delay between tuning cycles

It's observed that i.MX uSDHC needed delay between tuning
cycles for HS200 successful tuning. This patch is to set 1ms
delay for that.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>