qemu_monitor: implement query-cpu-model-comparison

qemu_monitor: implement query-cpu-model-comparison

Interfaces with QEMU to compare CPU models. The command takes two CPU
models, A and B, that are given a model name and an optional list of
CPU features. Through the query-cpu-model-comparison command issued
via QMP, a result is produced that contains the comparison evaluation
string (identical, superset, subset, incompatible).

The list of properties (aka CPU features) that is returned from the QMP
response is ignored.

Signed-off-by: Collin Walling <walling@linux.ibm.com>
Reviewed-by: Daniel Henrique Barboza <danielh413@gmail.com>
Message-Id: <1568924706-2311-12-git-send-email-walling@linux.ibm.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>