mmc: omap_hsmmc: stop using ->enable|disable() callbacks

The ->enable|disable() callbacks are only used to get and put runtime
PM references. Currently omap_hsmmc's ->set_ios() already does this
itself.

Other host drivers deals with runtime PM without using the
->enable|disable() callbacks and thus do the runtime PM reference
counting themselves. Apply that approach for omap_hsmmc as well and
then discard the ->enable|disable() callbacks.

Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>