register a "CpusAccel" interface for HVF as well.

Signed-off-by: Claudio Fontana <cfontana@suse.de>
Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
[added const]
Signed-off-by: Claudio Fontana <cfontana@suse.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>