MN10300: Cache: Implement SMP global cache flushing

Implement SMP global cache flushing for MN10300.  This will be used by the AM34
which is SMP capable.

Signed-off-by: Akira Takeuchi <takeuchi.akr@jp.panasonic.com>
Signed-off-by: Kiyoshi Owada <owada.kiyoshi@jp.panasonic.com>
Signed-off-by: David Howells <dhowells@redhat.com>