arm: Add xlnx-ep108 machine

arm: Add xlnx-ep108 machine

Add a machine model for the Xilinx ZynqMP SoC EP108 board.

Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Tested-by: Alistair Francis <alistair.francis@xilinx.com>
Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Message-id: 3896b34c862f370dc0679e4428bf3848d1f9f83c.1431381507.git.peter.crosthwaite@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>