mmc: sdhci: let GPIO based card detection have higher precedence

Controller could have BROKEN_CARD_DETECTION quirk set, but drivers
could use GPIO to detect card present state. Let, when defined, GPIO
take precedence, so drivers could properly detect card state and not
use polling.

Signed-off-by: Ivan T. Ivanov <ivan.ivanov@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>