i386/hyperv: error out if features requested but unsupported

i386/hyperv: error out if features requested but unsupported

In order to guarantee compatibility on migration, QEMU should have
complete control over the features it announces to the guest via CPUID.

However, for a number of Hyper-V-related cpu properties, if the
corresponding feature is not supported by the underlying KVM, the
propery is silently ignored and the feature is not announced to the
guest.

Refuse to start with an error instead.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Message-Id: <20180330170209.20627-3-rkagan@virtuozzo.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>