OCTEON chips with the CIU3 interrupt controller use a different IPI
mechanism that previous models.

Add plat_smp_ops for the cn78xx and probing code to choose between the
two types of ops.
Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12499/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>