MIPS: Octeon: Move MSI code out of octeon-irq.c.

Put all the MSI code in one place (msi-octeon.c).  This simplifies
octeon-irq.c and gets rid of some ugly #ifdefs

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1484/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>