pinctrl: sh-pfc: r8a7796: Add EtherAVB pins, groups and functions

This patch adds AVB_LINK, AVB_MAGIC, AVB_PHY_INT, AVB_MDC, AVB_AVTP_PPS,
AVB_AVTP_MATCH, AVB_AVTP_CAPTURE pins, groups and functions to R8A7796
SoC.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>