ubifs: Modify ubifs u-boot wrapper function prototypes for generic fs use

Modify the ubifs u-boot wrapper function prototypes for generic fs use,
and give them their own header file.

This is a preparation patch for adding ubifs support to the generic fs
code from fs/fs.c.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
diff --git a/common/cmd_ubifs.c b/common/cmd_ubifs.c
index 8e9a4e5..5e9d357 100644
--- a/common/cmd_ubifs.c
+++ b/common/cmd_ubifs.c
@@ -15,8 +15,7 @@
 #include <common.h>
 #include <config.h>
 #include <command.h>
-
-#include "../fs/ubifs/ubifs.h"
+#include <ubifs_uboot.h>
 
 static int ubifs_initialized;
 static int ubifs_mounted;
@@ -54,14 +53,7 @@
 
 void cmd_ubifs_umount(void)
 {
-
-	if (ubifs_sb) {
-		printf("Unmounting UBIFS volume %s!\n",
-		       ((struct ubifs_info *)(ubifs_sb->s_fs_info))->vi.name);
-		ubifs_umount(ubifs_sb->s_fs_info);
-	}
-
-	ubifs_sb = NULL;
+	uboot_ubifs_umount();
 	ubifs_mounted = 0;
 	ubifs_initialized = 0;
 }