mmc: sdhci-pci: Add Bay Trail and Braswell SD card detect

Add support for card detect for Bay Trail
and Braswell SD Card host controllers in PCI
mode.

This uses the gpio descriptor API which can find
gpio descriptors, for example, on an ACPI comapnion
device.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>