OvmfPkg: QemuBootOrderLib: widen ParseUnitAddressHexList() to UINT64
    
    The OpenFirmware device path nodes that QEMU generates for virtio-mmio
    transports contain 64-bit hexadecimal values (16 nibbles) -- the base
    addresses of the register blocks. In order to parse them soon,
    ParseUnitAddressHexList() must parse UINT64 values.
    
    Call sites need to be adapted, as expected.
    
    Contributed-under: TianoCore Contribution Agreement 1.0
    Signed-off-by: Laszlo Ersek <lersek@redhat.com>
    Acked-by: Jordan Justen <jordan.l.justen@intel.com>
    
    git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16574 6f19259b-4bc3-4df7-8a09-765794883524