Move and rename accel/qtest/qtest-cpus.c files to accel/dummy-cpus.c so
it can be re-used by Xen.

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
Message-Id: <20201013140511.5681-3-jandryuk@gmail.com>
Reviewed-by: Claudio Fontana <cfontana@suse.de>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>