hw/intc: Only build the xlnx-iomod-intc device for the MicroBlaze PMU

hw/intc: Only build the xlnx-iomod-intc device for the MicroBlaze PMU

The Xilinx I/O Module Interrupt Controller is only used by the
MicroBlaze PMU, not by the AArch64 machine.
Move it from the generic ZynqMP object list to the PMU specific.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190427141459.19728-3-philmd@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>