net: fec: don't access RACC register when not available

Not all silicon implementations of the Freescale FEC hardware module
have the RACC (Receive Accelerator Function) register, so we should not
be trying to access it on those that don't. Currently none of the ColdFire
based parts with a FEC have it.

Support for RACC was introduced by commit 4c09eed9 ("net: fec: Enable imx6
enet checksum acceleration"). A fix was introduced in commit d1391930


("net: fec: Fix build for MCF5272") that disables its use on the ColdFire
M5272 part, but it doesn't fix the general case of other ColdFire parts.

To fix we create a quirk flag, FEC_QUIRK_HAS_RACC, and check it before
working with the RACC register.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: David S. Miller <davem@davemloft.net>