mmc: sdhci-msm: Add HS400 platform support

The following msm platform specific changes are added to support HS400.
- Allow tuning for HS400 mode.
- Configure HS400 timing mode using the VENDOR_SPECIFIC_FUNC register.

Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>