net: fec: enable hardware checksum only on imx6q-fec

net: fec: enable hardware checksum only on imx6q-fec

Commit 19896b4 (net: fec: Enable imx6 enet checksum acceleration.)
enables hardware checksum acceleration unconditionally for all fec
variants.  This is inappropriate, because some variants like imx5 have
no such support on hardware.  Consequently, fec is broken on these
platforms.  Fix it by enabling hardware checksum only on imx6q-fec type
of controllers.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Jim Baxter <jim_baxter@mentor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>