mmc: core: Disable card detect during shutdown

It's seems prone to problems by allowing card detect and its corresponding
mmc_rescan() work to run, during platform shutdown. For example, we may end
up turning off the power while initializing a card, which potentially could
damage it.

To avoid this scenario, let's add ->shutdown_pre() callback for the mmc host
class device and then turn of the card detect from there.

Reported-by: Al Cooper <alcooperx@gmail.com>
Suggested-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211203141555.105351-1-ulf.hansson@linaro.org