xfs: consolidate xfs_rename.c

Move the rename code to xfs_inode.c to continue consolidating
all the kernel xfs_inode operations in the one place.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>