MMC core already has support for HS400.  Add HS400
support to SDHCI driver.  The SDHC Standard specification
does not define HS400 so consequently HS400 support is
non-standard.  However HS400 is not selected without
the host controller setting the corresponding capability
flags so host controllers not yet supporting HS400
will not be affected.  To support that, a quirk
SDHCI_QUIRK2_CAPS_BIT63_FOR_HS400 is introduced to
enable the use of capabilities register reserved bit-63
to indicate HS400 support.

Because HS400 is non-standard for SDHCI, it is possible
that different vendors will do things in different ways.
However HS200 support faced the same issue but currently
there is only one solution.  As such, no attempt has
been made to provide for alternate HS400 solutions except
for SDHCI_QUIRK2_CAPS_BIT63_FOR_HS400.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>