cpuid: don't setup USB devices

The CPUID dump test kernel doesn't need USB devices.

This allows some older QEMU versions to be tested.
Signed-off-by: NEduardo Habkost <ehabkost@raisama.net>

qemu/tests/cfg/qemu_cpu.cfg

@@ -6,6 +6,8 @@
     kill_vm = yes
     kill_vm_gracefully = no
     smp = 1
+    usbs =
+    usb_devices =
 
     # ask autotest to not mess with the cpu_model settings
     auto_cpu_model = no