ravb: ptp: Add CONFIG mode support

This patch makes PTP support active in CONFIG mode on R-Car Gen3.

Signed-off-by: Kazuya Mizuguchi <kazuya.mizuguchi.ks@renesas.com>
Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>