dt-bindings: net: renesas,etheravb: Add r8a779g0 support

Document support for the Renesas Ethernet AVB (EtherAVB-IF) block in the
Renesas R-Car V4H (R8A779G0) SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>