mmc: omap_hsmmc: use mmc_of_parse to parse common mmc configuration.

This ensures that all standard options are available to hsmmc,
In particular, I need cap-power-off-card.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>