mmc: sdhci-pci: Add support for drive strength selection for SPT

Implement the select_drive_strength callback to provide
drive strength selection for Intel SPT.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
diff --git a/include/linux/mmc/sdhci-pci-data.h b/include/linux/mmc/sdhci-pci-data.h
index 8959604..fda15b6 100644
--- a/include/linux/mmc/sdhci-pci-data.h
+++ b/include/linux/mmc/sdhci-pci-data.h
@@ -15,4 +15,6 @@
 extern struct sdhci_pci_data *(*sdhci_pci_get_data)(struct pci_dev *pdev,
 				int slotno);
 
+extern int sdhci_pci_spt_drive_strength;
+
 #endif