PCI: Set ROM shadow location in arch code, not in PCI core

IORESOURCE_ROM_SHADOW means there is a copy of a device's option ROM in
RAM.  The existence of such a copy and its location are arch-specific.
Previously the IORESOURCE_ROM_SHADOW flag was set in arch code, but the
0xC0000-0xDFFFF location was hard-coded into the PCI core.

If we're using a shadow copy in RAM, disable the ROM BAR and release the
address space it was consuming.  Move the location information from the PCI
core to the arch code that sets IORESOURCE_ROM_SHADOW.  Save the location
of the RAM copy in the struct resource for PCI_ROM_RESOURCE.

After this change, pci_map_rom() will call pci_assign_resource() and
pci_enable_rom() for these IORESOURCE_ROM_SHADOW resources, which we did
not do before.  This is safe because:

  - pci_assign_resource() will do nothing because the resource is marked
    IORESOURCE_PCI_FIXED, which means we can't move it, and

  - pci_enable_rom() will not turn on the ROM BAR's enable bit because the
    resource is marked IORESOURCE_ROM_SHADOW, which means it is in RAM
    rather than in PCI memory space.

Storing the location in the struct resource means "lspci" will show the
shadow location, not the value from the ROM BAR.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>