pinctrl: sh-pfc: r8a77965: Add EtherAVB groups/functions

Add EtherAVB groups and functions definitions for R-Car M3-N.

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>