net: atlantic: put ptp code under IS_REACHABLE check

A1 requires additional processing for both egress and ingress to support
PTP.
And it makes sense to get rid of this processing altogether (via ifdef),
if PTP clock is disabled globally.

This patch puts the PTP code under the corresponding IS_REACHABLE check.

Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: Mark Starovoytov <mstarovoitov@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>