OvmfPkg/OvmfXen: remove IncompatiblePciDeviceSupport DXE driver
    
    The entry point function of "OvmfPkg/IncompatiblePciDeviceSupportDxe",
    namely DriverInitialize()
    [OvmfPkg/IncompatiblePciDeviceSupportDxe/IncompatiblePciDeviceSupport.c],
    bails out immediately if "PcdPciDisableBusEnumeration" is TRUE.
    
    The OvmfXen platform statically assigns this PCD TRUE. Thus, remove the
    driver from the OvmfXen platform.
    
    Cc: Anthony Perard <anthony.perard@citrix.com>
    Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
    Cc: Jordan Justen <jordan.l.justen@intel.com>
    Cc: Julien Grall <julien@xen.org>
    Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
    Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2122
    Signed-off-by: Laszlo Ersek <lersek@redhat.com>