Octeon has an boot-time option to disable pcie.

Since MSI depends on PCI-E, we should also disable MSI also with
this option is on in order to avoid inadvertently accessing PCIe
registers.
Signed-off-by: YunQiang Su <ysu@wavecomp.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: pburton@wavecomp.com
Cc: linux-mips@vger.kernel.org
Cc: aaro.koskinen@iki.fi
Cc: stable@vger.kernel.org # v3.3+