x86/PCI: Coalesce multiple overlapping host bridge windows

Previously we coalesced windows by expanding the first overlapping one and
making the second invalid.  But we never look at the expanded first window
again, so we fail to notice other windows that overlap it.  For example, we
coalesced these:

  [io  0x0000-0x03af] // #0
  [io  0x03e0-0x0cf7] // #1
  [io  0x0000-0xdfff] // #2

into these, which still overlap:

  [io  0x0000-0xdfff] // #0
  [io  0x03e0-0x0cf7] // #1

The fix is to expand the *second* overlapping resource and ignore the
first, so we get this instead with no overlaps:

  [io  0x0000-0xdfff] // #2

[bhelgaas: changelog]
Reference: https://bugzilla.kernel.org/show_bug.cgi?id=62511


Signed-off-by: Alexey Neyman <stilor@att.net>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>