ARM: dts: r9a06g032-rzn1d400-db: Add switch description

ARM: dts: r9a06g032-rzn1d400-db: Add switch description

Add the description for the switch, GMAC2 and MII converter.  With these
definitions, the switch ports 0 and 1 (MII ports 5 and 4) are working on
the RZ/N1D-DB board.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20220624144001.95518-16-clement.leger@bootlin.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>