am33xx: define syscon control module device node

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Reviewed-by: Wolfram Sang <wsa@the-dreams.de>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: David S. Miller <davem@davemloft.net>