mmc: sdhci: add the get_cd callback function in sdhci_ops

Some SoCs can have their own card dect scheme.
Then they may use this get_cd callback function after implementing init
in their drivers.
Signed-off-by: NJaehoon Chung <jh80.chung@samsung.com>

include/sdhci.h

@@ -235,6 +235,7 @@ struct sdhci_ops {
 	void            (*write_w)(struct sdhci_host *host, u16 val, int reg);
 	void            (*write_b)(struct sdhci_host *host, u8 val, int reg);
 #endif
+	int		(*get_cd)(struct sdhci_host *host);
 };
 
 struct sdhci_host {