OvmfPkg: QemuBootOrderLib: recognize extra PCI root buses

The OFW device path that QEMU exports in the "bootorder" fw_cfg file, for
a device that is plugged into the main PCI root bus, is:

  /pci@i0cf8/...

Whereas the same device plugged into the N'th extra root bus results in:

  /pci@i0cf8,N/pci-bridge@0/...

(N is in hex.)

Extend TranslatePciOfwNodes() so that it not assume a single PCI root;
instead it parse the extra root bus serial number if present, and resolve
it in the translation to the UEFI devpath fragment.

Note that the "pci-bridge@0" node is a characteristic of QEMU's PXB
device. It reflects the actual emulated PCI hierarchy. We don't parse it
specifically in this patch, because it is automatically handled by the
bridge sequence translator added recently in SVN rev 17385 (git commit
feca17fa4b) -- "OvmfPkg: QemuBootOrderLib: parse OFW device path nodes of
PCI bridges".

The macro EXAMINED_OFW_NODES need not be raised from 6. The longest OFW
device paths that we wish to recognize under this new scheme comprise 5
nodes. The initial "extra root bus" OFW fragment, visible at the top,
takes up 2 nodes, after which the longest device-specific patterns (IDE
disk, IDE CD-ROM, ISA floppy, virtio-scsi disk) take 3 more nodes each.

Cc: Jordan Justen <jordan.l.justen@intel.com>
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@17965 6f19259b-4bc3-4df7-8a09-765794883524

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