mmc: sdhci: Add sd host v4 mode

For SD host controller version 4.00 or later ones, there're two
modes of implementation - Version 3.00 compatible mode or
Version 4 mode.  This patch introduced an interface to enable
v4 mode.

Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>