ARM: mvebu: make use of of_find_matching_node_and_match

Instead of the of_find_matching_node()/of_match_node() pair, which requires two
iterations through the match table, make use of of_find_matching_node_and_match(),
which only iterates through the table once.

While we're here, mark the of_system_controller table const.

Signed-off-by: Josh Cartwright <joshc@codeaurora.org>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>