mmc: sdhci: Remove redundant runtime PM calls

Commit 9250aea7 ("mmc: core: Enable runtime PM management of host
devices"), made some calls to the runtime PM API from the driver
redundant. Especially those which deals with runtime PM reference
counting, so let's remove them.

Moreover as SDHCI have its own wrapper functions for runtime PM these
becomes superfluous, so let's remove them as well.

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