ARM: dts: r9a06g032: Describe MII converter

Add the MII converter node which describes the MII converter that is
present on the RZ/N1 SoC.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20220624144001.95518-13-clement.leger@bootlin.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>