7570a333 ("PCI: Add pcie_hp=nomsi to disable MSI/MSI-X for pciehp
driver") added the "pcie_hp=nomsi" kernel parameter to work around this
error on shutdown:

  irq 16: nobody cared (try booting with the "irqpoll" option)
  Pid: 1081, comm: reboot Not tainted 3.2.0 #1
  ...
  Disabling IRQ #16

This happened on an unspecified system (possibly involving the Integrated
Device Technology, Inc. Device 807f bridge) where "an un-wanted interrupt
is generated when PCI driver switches from MSI/MSI-X to INTx while shutting
down the device."

The implication was that the device was buggy, but it is normal for a
device to use INTx after MSI/MSI-X have been disabled.  The only problem
was that the driver was still attached and it wasn't prepared for INTx
interrupts.  Prarit Bhargava fixed this issue with fda78d7a ("PCI/MSI:
Stop disabling MSI/MSI-X in pci_device_shutdown()").

There is no automated way to set this parameter, so it's not very useful
for distributions or end users.  It's really only useful for debugging, and
we have "pci=nomsi" for that purpose.

Revert 7570a333 to remove the "pcie_hp=nomsi" parameter.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
CC: MUNEDA Takahiro <muneda.takahiro@jp.fujitsu.com>
CC: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
CC: Prarit Bhargava <prarit@redhat.com>