wcxb: Disable presence detect reporting on upstream port during PCIe hard reset.

When the card goes through a reset the PCIe link will be brought down. Some
slots will report this change upstream to the root port which will believe that
the card has been hotplugged out of the system.

This fixes cases on some systems where, during a firmware update, the card gets
removed from the system's logical PCI tree with messages like the following in
the kernel log:

  pciehp 0000:00:1c.0:pcie04: Card not present on Slot(259)
  pciehp 0000:00:1c.0:pcie04: Card present on Slot(259)

Internal-Issue-ID: DAHDI-1091
Signed-off-by: Shaun Ruffell <sruffell@digium.com>