mmc: sdhci: Allow override of mmc host operations

mmc: sdhci: Allow override of mmc host operations

commit bf60e592a1af4d6f65dd54593250183f14360eed upstream.

In the past, fixes for specific hardware devices were implemented
in sdhci using quirks.  That approach is no longer accepted because
the growing number of quirks was starting to make the code difficult
to understand and maintain.

One alternative to quirks, is to allow drivers to override the default
mmc host operations.  This patch makes it easy to do that, and it is
needed for a subsequent bug fix, for which separate patches are
provided.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>