mmc: sdhci: Add HS400 host layer support

HS400 bus speed mode also requires tuning to be performed as done in
HS200 mode. Add the capability in host layer to perform tuning for
HS400 too.

Change-Id: I4508739dd76b1aca79f0c975fb31010c6f8ba9df
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>