arm64: dts: renesas: r8a7796: Add CMT device nodes

This patch adds CMT{0|1|2|3} device nodes for r8a7796 SoC.

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