fs: Create a common fs_devread for ext4/reiserfs/zfs

The ext4, reiserfs and zfs filesystems all have their own implementation
of the same function, *_devread. Generalize this function into fs_devread
and put the code into fs/fs_internal.c.

Signed-off-by: Marek Behun <marek.behun@nic.cz>
[trini: Move fs/fs_internal.o hunk to the end of fs/Makefile as all
cases need it]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/fs_internal.h b/include/fs_internal.h
new file mode 100644
index 0000000..9d6dddd
--- /dev/null
+++ b/include/fs_internal.h
@@ -0,0 +1,17 @@
+/*
+ * 2017 by Marek Behun <marek.behun@nic.cz>
+ *
+ * Derived from code in ext4/dev.c, which was based on reiserfs/dev.c
+ *
+ * SPDX-License-Identifier:	GPL-2.0
+ */
+
+#ifndef __U_BOOT_FS_INTERNAL_H__
+#define __U_BOOT_FS_INTERNAL_H__
+
+#include <part.h>
+
+int fs_devread(struct blk_desc *, disk_partition_t *, lbaint_t, int, int,
+	       char *);
+
+#endif /* __U_BOOT_FS_INTERNAL_H__ */