move inode tracing out of xfs_vnode.

Move the inode tracing into xfs_iget.c / xfs_inode.h and kill xfs_vnode.c
now that it's empty.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Niv Sardi <xaiki@sgi.com>