MIPS: Octeon: Add PCIe link status check

MIPS: Octeon: Add PCIe link status check

The standard PCIe configuration read-write interface is used to
access the configuration space of the peripheral PCIe devices
of the mips processor after the PCIe link surprise down, it can
generate kernel panic caused by "Data bus error". So it is
necessary to add PCIe link status check for system protection.
When the PCIe link is down or in training, assigning a value
of 0 to the configuration address can prevent read-write behavior
to the configuration space of peripheral PCIe devices, thereby
preventing kernel panic.

Signed-off-by: Songyang Li <leesongyang@outlook.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>