Print the IRQ used by PCIe Link Bandwidth Notification services port as
AER, PME and DPC do.  It provides convenience to track PCIe BW notification
interrupt counts of certain port from /proc/interrupts.

The dmesg log is as below:

  pcieport 0000:00:00.0: bw_notification: enabled with IRQ 1166

Link: https://lore.kernel.org/r/1599737055-73624-1-git-send-email-liudongdong3@huawei.comSigned-off-by: Dongdong Liu <liudongdong3@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>