printk: Add a DEPRECATED macro

sctp has several points in its setsockopt path in which it issues deprecation
warnings.  It seems like it might be handy to macrotize such a warning so other
subsystems can use it easily

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: "David S. Miller" <davem@davemloft.net>
CC: linux-kernel@vger.kernel.org
CC: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>