arm/arm64: rename smp_run to on_cpus

Also base on on_cpu_async() to allow it to be called more than once.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Message-Id: <20170601135002.26704-4-drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>