mmc: sdhci: Add a callback to select drive strength

Add a callbak to let host drivers select drive
strength.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
index 923ff22..5521d29 100644
--- a/drivers/mmc/host/sdhci.h
+++ b/drivers/mmc/host/sdhci.h
@@ -538,6 +538,10 @@
 	void	(*platform_init)(struct sdhci_host *host);
 	void    (*card_event)(struct sdhci_host *host);
 	void	(*voltage_switch)(struct sdhci_host *host);
+	int	(*select_drive_strength)(struct sdhci_host *host,
+					 struct mmc_card *card,
+					 unsigned int max_dtr, int host_drv,
+					 int card_drv, int *drv_type);
 };
 
 #ifdef CONFIG_MMC_SDHCI_IO_ACCESSORS