xlnx-zynqmp: Connect the SPI devices

xlnx-zynqmp: Connect the SPI devices

Connect the Xilinx SPI devices to the ZynqMP model.

Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
[ PC changes
 * Use QOM alias for bus connectivity on SoC level
]
Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
[PMM: free the g_strdup_printf() string when finished with it]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>