net: fec: Let fec_ptp have its own interrupt routine

This is better for code locality and should slightly
speed up normal interrupts.

This also allows PPS clock output to start working for
i.mx7. This is because i.mx7 was already using the limit
of 3 interrupts, and needed another.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Acked-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>