xlnx-zcu102: Add a machine level virtualization property

xlnx-zcu102: Add a machine level virtualization property

Add a machine level virtualization property. This defaults to false and can be
set to true using this machine command line argument:
    -machine xlnx-zcu102,virtualization=on

This follows what the ARM virt machine does.

This property only applies to the ZCU102 machine. The EP108 machine does
not have this property.

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>