hvf: Add missing include

hvf: Add missing include

The sysemu/accel.h header is needed for the ACCEL_CLASS_NAME
macro.  This will be necessary to allow us to use OBJECT_DEFINE*()
for TYPE_HVF_ACCEL.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Tested-By: Roman Bolshakov <r.bolshakov@yadro.com>
Message-Id: <20200825192110.3528606-14-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>