qemu: qmp query-cpu-model-expansion command

query-cpu-model-expansion is used to get a list of features for a given cpu
model name or to get the model and features of the host hardware/environment
as seen by Qemu/kvm.

Signed-off-by: Collin L. Walling <walling@linux.vnet.ibm.com>
Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>