mips: octeon: Add Octeon PCIe host controller driver

This patch adds the PCIe host controller driver for MIPS Octeon II/III.
The driver mainly consist of the PCI config functions, as all of the
complex serdes related port / lane setup, is done in the serdes / pcie
code available in the "arch/mips/mach-octeon" directory.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Aaron Williams <awilliams@marvell.com>
Cc: Chandrakala Chavva <cchavva@marvell.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>