ARM: dts: iwg20d-q7: Add support for iWave G20D-Q7 board based on RZ/G1M

Add support for iWave RainboW-G20D-Qseven board based on RZ/G1M.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Chris Paterson <chris.paterson2@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>