PS2 devices only work on X86 platform, other platforms may need
USB devices instead. Athough it doesn't influence the QEMU command line,
it's not right to add PS2 mouse/keyboard for non-X86 platform.
Signed-off-by: NLi Zhang <zhlcindy@linux.vnet.ibm.com>
Signed-off-by: NJán Tomko <jtomko@redhat.com>