net: fec: add interrupt coalesc quirk flag

Different i.MX SOC FEC support different features like :
- i.MX6Q/DL FEC does not support AVB and interrupt coalesc
- i.MX6SX/i.MX7D supports AVB and interrupt coalesc
- i.MX6UL/ULL does not support AVB, but support interrupt coalesc

So, add new quirk flag to judge the supported features.

Signed-off-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>