mmc: sdhci: fix card detection code

There are certain cases where the card detect gpio is not handled properly
when broken card detection quirk is used.

Currently the code enables polling irrespective of the presence of card
detect gpio when broken card detect quirk is enabled. Instead only enable
polling when the card detect gpio is missing along with the quirk.

Also when checking for the card detect status, check for the presence or
absence of a valid gpio before assuming that the card is always present.

Change-Id: I178b22031704ff102602271ae4ad16e30f14778f
Signed-off-by: Krishna Konda <kkonda@codeaurora.org>