Make use of mmc core support for re-tuning instead
of doing it all in the sdhci driver.

This patch also changes to flag the need for re-tuning
always after runtime suspend when tuning has been used
at initialization. Previously it was only done if
the re-tuning timer was in use.
Signed-off-by: NAdrian Hunter <adrian.hunter@intel.com>
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>