ARM: dts: iwg20d-q7-common: Move cmt/rwdt node out of RZ/G1M SOM

The iWave RZ/G1N board is almost identical to RZ/G1M. cmt and rwdt modules
are SoC specific and should be part of board dts rather than SoM dtsi. By
moving these nodes to the common dtsi it allows cmt and rwdt to be enabled
on both of these boards with less lines of code.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>