clk: renesas: r8a779g0: Add EtherAVB clocks

Add the module clocks used by the Ethernet AVB (EtherAVB-IF) blocks on
the Renesas R-Car V4H (R8A779G0) SoC.

Based on a larger patch in the BSP by Kazuya Mizuguchi.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/e9382b0d9acc84acc2357a6921a1459f3a32240e.1662714852.git.geert+renesas@glider.be