PCI/MSI: Stop disabling MSI/MSI-X in pci_device_shutdown()

The pci_bus_type .shutdown method, pci_device_shutdown(), is called from
device_shutdown() in the kernel restart and shutdown paths.

Previously, pci_device_shutdown() called pci_msi_shutdown() and
pci_msix_shutdown().  This disables MSI and MSI-X, which causes the device
to fall back to raising interrupts via INTx.  But the driver is still bound
to the device, it doesn't know about this change, and it likely doesn't
have an INTx handler, so these INTx interrupts cause "nobody cared"
warnings like this:

  irq 16: nobody cared (try booting with the "irqpoll" option)
  CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.8.2-1.el7_UNSUPPORTED.x86_64 #1
  Hardware name: Hewlett-Packard HP Z820 Workstation/158B, BIOS J63 v03.90 06/
  ...

The MSI disabling code was added by d52877c ("pci/irq: let
pci_device_shutdown to call pci_msi_shutdown v2") because a driver left MSI
enabled and kdump failed because the kexeced kernel wasn't prepared to
receive the MSI interrupts.

Subsequent commits 1851617 ("PCI/MSI: Disable MSI at enumeration even
if kernel doesn't support MSI") and  e80e7ed ("PCI/MSI: Initialize MSI
capability for all architectures") changed the kexeced kernel to disable
all MSIs itself so it no longer depends on the crashed kernel to clean up
after itself.

Stop disabling MSI/MSI-X in pci_device_shutdown().  This resolves the
"nobody cared" unhandled IRQ issue above.  It also allows PCI serial
devices, which may rely on the MSI interrupts, to continue outputting
messages during reboot/shutdown.

[bhelgaas: changelog, drop pci_msi_shutdown() and pci_msix_shutdown() calls
altogether]
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=187351
Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Alex Williamson <alex.williamson@redhat.com>
CC: David Arcari <darcari@redhat.com>
CC: Myron Stowe <mstowe@redhat.com>
CC: Lukas Wunner <lukas@wunner.de>
CC: Keith Busch <keith.busch@intel.com>
CC: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/pci/pci-driver.c

@@ -461,8 +461,6 @@ static void pci_device_shutdown(struct device *dev)
 
 	if (drv && drv->shutdown)
 		drv->shutdown(pci_dev);
-	pci_msi_shutdown(pci_dev);
-	pci_msix_shutdown(pci_dev);
 
 	/*
 	 * If this is a kexec reboot, turn off Bus Master bit on the