xlnx-zcu102: Manually create the machines

xlnx-zcu102: Manually create the machines

In preperation for future work let's manually create the Xilnx machines.
This will allow us to set properties for the machines in the future.

Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>