ravb: Exclude gPTP feature support for RZ/G2L

R-Car supports gPTP feature whereas RZ/G2L does not support it.
This patch excludes gtp feature support for RZ/G2L.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>