mmc: add mmc_poll_for_busy() and change the purpose of mmc_send_status()

mmc_send_status() is currently used to poll the card until it is ready, not
actually returning the status of the card.
Make it return the status and add another function to poll the card.

Also remove the 'extern' declaration in the mmc-private.h header to comply
with the coding standard.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
diff --git a/drivers/mmc/mmc_private.h b/drivers/mmc/mmc_private.h
index f49b6eb..35170d0 100644
--- a/drivers/mmc/mmc_private.h
+++ b/drivers/mmc/mmc_private.h
@@ -11,10 +11,11 @@
 
 #include <mmc.h>
 
-extern int mmc_send_cmd(struct mmc *mmc, struct mmc_cmd *cmd,
-			struct mmc_data *data);
-extern int mmc_send_status(struct mmc *mmc, int timeout);
-extern int mmc_set_blocklen(struct mmc *mmc, int len);
+int mmc_send_cmd(struct mmc *mmc, struct mmc_cmd *cmd, struct mmc_data *data);
+int mmc_send_status(struct mmc *mmc, unsigned int *status);
+int mmc_poll_for_busy(struct mmc *mmc, int timeout);
+
+int mmc_set_blocklen(struct mmc *mmc, int len);
 #ifdef CONFIG_FSL_ESDHC_ADAPTER_IDENT
 void mmc_adapter_card_type_ident(void);
 #endif