mmc: sdhci-pci: Respect PM flags when enabling card detect GPIO IRQ wakeup

Commit 03dbaa04 ("mmc: slot-gpio: Add support to enable irq wake on
cd_irq") enabled wakeup at initialization. However, users also want to
control it from sysfs power/wakeup attribute. That means the driver needs
to check the PM flags before enabling it in the suspend callback. Add
support for that in sdhci-pci, which is the only driver presently using the
MMC_CAP_CD_WAKE flag, and remove the enabling in mmc_gpiod_request_cd_irq()

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