serial: serial_octeon_bootcmd.c: Add PCI remote console support

serial: serial_octeon_bootcmd.c: Add PCI remote console support

This patch adds the PCI bootcmd feature for MIPS Octeon, which will be
used by the upcoming Octeon III NIC23 board support. It enables the use
of the "oct-remote-load" and "oct-remote-bootcmd" on host PC's to
communicate with the PCIe target and load images into the onboard
memory and issue commands.

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>