PCI/LINK: Disable bandwidth notification interrupt during suspend

If the bandwidth notification interrupt is left unmasked when entering
suspend to idle, it triggers immediately bringing the system back to
working state.

To keep that from happening, disable the interrupt when entering system
sleep and enable it again during resume.

Reported-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>