MIPS: Octeon: Disallow MSI-X interrupt and fall back to MSI interrupts.

MSI-X interrupts are not supported yet for Octeon, return error if
MSI-X interrupts are requested by driver so that the driver will fall
back to use MSI interrupts.

Signed-off-by: Chandrakala Chavva <cchavva@caviumnetworks.com>
To: linux-mips@linux-mips.org
Cc: David Daney <ddaney@caviumnetworks.com>
Patchwork: https://patchwork.linux-mips.org/patch/1506/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: David Daney <ddaney@caviumnetworks.com>