qemu: Separate partial CPU check into a function

qemu: Separate partial CPU check into a function

The new qemuDomainCheckCPU function is used as a replacement for
virCPUCompare to make sure all callers use the same comparison
algorithm. As a side effect qemuConnectCompareHypervisorCPU now properly
reports CPU compatibility for CPU model that are considered runnable by
QEMU even if our definition of the model disagrees.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>