PCI: Don't attempt to claim shadow copies of ROM

If we're using a shadow copy of a PCI device ROM, the shadow copy is in RAM
and the device never sees accesses to it and doesn't respond to it.  We
don't have to route the shadow range to the PCI device, and the device
doesn't have to claim the range.

Previously we treated the shadow copy as though it were the ROM BAR, and we
failed to claim it because the region wasn't routed to the device:

  pci 0000:01:00.0: Video device with shadowed ROM at [mem 0x000c0000-0x000dffff]
  pci_bus 0000:01: Allocating resources
  pci 0000:01:00.0: can't claim BAR 6 [mem 0x000c0000-0x000dffff]: no compatible bridge window

The failure path of pcibios_allocate_dev_rom_resource() cleared out the
resource start address, which also caused the following ioremap() warning:

  WARNING: CPU: 0 PID: 116 at /build/linux-akdJXO/linux-4.8.0/arch/x86/mm/ioremap.c:121 __ioremap_caller+0x1ec/0x370
  ioremap on RAM at 0x0000000000000000 - 0x000000000001ffff

Handle an option ROM shadow copy as RAM, without trying to insert it into
the iomem resource tree.

This fixes a regression caused by 0c0e0736 ("PCI: Set ROM shadow
location in arch code, not in PCI core"), which appeared in v4.6.  The
regression causes video device initialization to fail.  This was reported
on AMD Turks, but it likely affects others as well.

Fixes: 0c0e0736 ("PCI: Set ROM shadow location in arch code, not in PCI core")
Reported-and-tested-by: Vecu Bosseur <vecu.bosseur@gmail.com>
Link: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1627496
Link: https://bugzilla.kernel.org/show_bug.cgi?id=175391
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1352272


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org	# v4.6+