The configuration data provided by an MCFG entry, i.e., PCI segment and bus
range, may span multiple host bridges.

pci_mcfg_lookup() previously required an exact match of the host bridge
starting bus and the MCFG starting bus, which made the following
configuration fail:

  MCFG region:
    segment: 0
    bus range: 0x00-0xff

  host bridge
    segment: 0
    bus range: 0x20-0x4f

Relax the bus range check in pci_mcfg_lookup() so we can use any MCFG entry
that contains the required bus range, as we do in pci_mmconfig_lookup().

[bhelgaas: changelog]
Signed-off-by: Zhou Wang <wangzhou1@hisilicon.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Tomasz Nowicki <tn@semihalf.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>