Ovfm/Xen: add a Vendor Hardware device path GUID for the XenBus root

Ovfm/Xen: add a Vendor Hardware device path GUID for the XenBus root

On non-PCI Xen guests (such as ARM), the XenBus root is not a PCI
device but an abstract 'platform' device. Add a dedicated Vendor
Hardware device path GUID to identify this node.

Contributed-under: TianoCore Contribution Agreement 1.0
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16978 6f19259b-4bc3-4df7-8a09-765794883524