MLK-11789 mmc: sdhci: Add 1ms delay in eMMC tuning procedure

On 4.1 kernel, some eMMC on i.MX7D-SDB board can't pass HS400 tuning,
the same eMMC can pass HS400 tuning on 3.14 kernel. The difference
is that 4.1 kernel does not have 1ms delay for eMMC during the
tuning procedure. The root cause still not find, add back the
1ms delay first.

Signed-off-by: Haibo Chen <haibo.chen@freescale.com>