OvmfPkg: QemuBootOrderLib: parse OFW device path nodes of PCI bridges

OvmfPkg: QemuBootOrderLib: parse OFW device path nodes of PCI bridges

When the Q35 machine type(s) of QEMU are used with libvirt, libvirt tends
to place some devices behind PCI bridges. This is then reflected in the
"bootorder" fw_cfg file. For example:

  /pci@i0cf8/pci-bridge@1e/pci-bridge@1/scsi@5/disk@0,0
  /pci@i0cf8/pci-bridge@1e/pci-bridge@1/scsi@3/channel@0/disk@0,0

As yet QemuBootOrderLib doesn't support such OFW device paths.

Add code that translates a sequence of pci-bridge nodes.

In practice libvirt seems to insert two such nodes (*), hence increment
EXAMINED_OFW_NODES with the same number.

(* Background, paraphrasing Laine Stump's words:

When the machine type is Q35, we create a dmi-to-pci bridge coming off of
the pcie root controller, and a pci-to-pci bridge coming off of that, then
attach most devices to the pci-to-pci bridge. This is done because you
can't hotplug into pcie-root, can't (or at least shouldn't) plug a
pci-to-pci bridge into pcie-root (so the next one has to be
dmi-to-pci-bridge), and can't hotplug into dmi-to-pci-bridge (so you need
to have a pci-to-pci bridge).)

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17385 6f19259b-4bc3-4df7-8a09-765794883524