mmc: sdhci-pci: add SDHCI_QUIRK2_HOST_OFF_CARD_ON for Medfield SDIO

SDIO is powered separately from the host controller, so the card can
remain on while the host controller is powered off during suspend.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>