i386: Don't automatically enable FEAT_KVM_HINTS bits

The assumption in the cpu->max_features code is that anything
enabled on GET_SUPPORTED_CPUID should be enabled on "-cpu host".
This shouldn't be the case for FEAT_KVM_HINTS.

This adds a new FeatureWordInfo::no_autoenable_flags field, that
can be used to prevent FEAT_KVM_HINTS bits to be enabled
automatically.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20180410211534.26079-1-ehabkost@redhat.com>
Tested-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>