ARM: dts: iwg20m: Enable cmt0

This patch enables cmt0 support from within the iwg20m SoM dtsi.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>