MIPS: Reorganize Cavium OCTEON PCI support.

Move the cavium PCI files to the arch/mips/pci directory.  Also cleanup
comment formatting and code layout.  Code from pci-common.c, was moved
into other files.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>