pinctrl: renesas: r8a779h0: Add AVB MII pins and groups

EtherAVB instances 0 and 1 support both RGMII and MII interfaces.
Add the missing pins and groups for MII.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/4a0a12227f2145ef53b18bc08f45b19dcd745fc6.1718378739.git.geert+renesas@glider.be