sdhci: acpi: add free_slot callback

The device specific resource can be free in free_slot after
removing host controller.

Signed-off-by: Wang Dongsheng <dongsheng.wang@hxt-semitech.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>