hw/microblaze: Do not allow xlnx-zynqmp-pmu-soc to be created by the user

hw/microblaze: Do not allow xlnx-zynqmp-pmu-soc to be created by the user

Using xlnx-zynqmp-pmu-soc on the command line causes QEMU to crash:

 ./qemu-system-microblazeel -M petalogix-ml605 -device xlnx-zynqmp-pmu-soc
 **
 ERROR:tcg/tcg.c:813:tcg_register_thread: assertion failed: (n < tcg_max_ctxs)
 Bail out!
 Aborted (core dumped)

Mark the device with "user_creatable = false" to avoid that this can happen.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2229
Message-ID: <20240322183153.1023359-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>