usb: new board-specific USB init interface

This commit unifies board-specific USB initialization implementations
under one symbol (usb_board_init), declaration of which is available in
usb.h.

New API allows selective initialization of USB controllers whenever needed.

Signed-off-by: Mateusz Zalega <m.zalega@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Lukasz Majewski <l.majewski@samsung.com>
diff --git a/drivers/usb/host/ohci.h b/drivers/usb/host/ohci.h
index d977e8f..9a4a2c2 100644
--- a/drivers/usb/host/ohci.h
+++ b/drivers/usb/host/ohci.h
@@ -19,14 +19,11 @@
 #endif /* CONFIG_SYS_OHCI_SWAP_REG_ACCESS */
 
 /* functions for doing board or CPU specific setup/cleanup */
-extern int usb_board_init(void);
-extern int usb_board_stop(void);
-extern int usb_board_init_fail(void);
+int usb_board_stop(void);
 
-extern int usb_cpu_init(void);
-extern int usb_cpu_stop(void);
-extern int usb_cpu_init_fail(void);
-
+int usb_cpu_init(void);
+int usb_cpu_stop(void);
+int usb_cpu_init_fail(void);
 
 static int cc_to_error[16] = {