net: mtk_eth_soc: mediatek: fix ppe flow accounting for v1 hardware

Older chips (like MT7622) use a different bit in ib2 to enable hardware
counter support. Add macros for both and select the appropriate bit.

Fixes: 3fbe4d8c ("net: ethernet: mtk_eth_soc: ppe: add support for flow accounting")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: David S. Miller <davem@davemloft.net>