mmc: enable/disable functions for SDIO

Like many other buses, the devices (functions) on the SDIO bus
must be enabled before they can be used. Add functions that allow
drivers to do so.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
diff --git a/include/linux/mmc/sdio_func.h b/include/linux/mmc/sdio_func.h
index 5c56df1..3365fef 100644
--- a/include/linux/mmc/sdio_func.h
+++ b/include/linux/mmc/sdio_func.h
@@ -55,6 +55,9 @@
 extern void sdio_claim_host(struct sdio_func *func);
 extern void sdio_release_host(struct sdio_func *func);
 
+extern int sdio_enable_func(struct sdio_func *func);
+extern int sdio_disable_func(struct sdio_func *func);
+
 extern unsigned char sdio_readb(struct sdio_func *func,
 	unsigned int addr, int *err_ret);