mmc: omap_hsmmc: use slot-gpio library for gpio support.

Using the common code removes some code duplication, and
makes it easier to switch to using mmc_of_parse() which
will remove more duplication.

This uses the new mmc_gpio_request_cd_isr to provide a non-standard
interrupt service routine for card-detect interrupts.

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