q35: fix mmconfig and PCI0._CRS

q35: fix mmconfig and PCI0._CRS

This patch changes the handling of the mmconfig area.  Thanks to the
pci(e) expander devices we already have the logic to exclude address
ranges from PCI0._CRS.  We can simply add the mmconfig address range
to the list get it excluded as well.

With that in place we can go with a fixed pci hole which covers the
whole area from the end of (low) ram to the ioapic.

This will make the whole logic alot less fragile.  No matter where the
firmware places the mmconfig xbar, things should work correctly.  The
guest also gets a bit more PCI address space (seabios boot):

    # cat /proc/iomem
    [ ... ]
    7ffdd000-7fffffff : reserved
    80000000-afffffff : PCI Bus 0000:00            <<-- this is new
    b0000000-bfffffff : PCI MMCONFIG 0000 [bus 00-ff]
      b0000000-bfffffff : reserved
    c0000000-febfffff : PCI Bus 0000:00
      f8000000-fbffffff : 0000:00:01.0
    [ ... ]

So this is a guest visible change.

Cc: László Érsek <lersek@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20190607073429.3436-1-kraxel@redhat.com>