cpu_x86: Disable blockers from unusable CPU models

cpu_x86: Disable blockers from unusable CPU models

When decoding CPUID data to virCPUDef we need to be careful about using
a CPU model which cannot be directly used on the current host. Normally,
libvirt would notice the features which prevent the model from being
usable and it would disable them in the computed virCPUDef, but this
won't work in case the definition of the CPU model in QEMU contains more
features than what we have in cpu_map.xml. We need to count with the
usability blockers we got from QEMU and explicitly disable all of them
to make the computed virCPUDef usable.

https://bugzilla.redhat.com/show_bug.cgi?id=1464832

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>