pciehp: workaround against Bad DLLP during power off

Set Bad DLLP Mask bit in Correctable Error Mask Register during
turning power off the slot.

This is the workaround against Bad DLLP error that sometimes happen
during turning power off on the slot which conforms to PCI Express
1.0a spec. The cause of this error seems that PCI Express 1.0a spec
doesn't have the following consideration that was added to PCI Express
1.1 spec.

    "If the port is associated with a hot-pluggable slot (Hot-Plug
    Capable bit in the Slot Capabilities register set to 1b), and
    Power Controller Control bit in Slot Control register is 1b(Off),
    then any transition to DL Inactive must not be considered an
    error."

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>