net: aquantia: disable ptp object build if no config

We do disable aq_ptp module build using inline
stubs when CONFIG_PTP_1588_CLOCK is not declared.

This reduces module size and removes unnecessary code.

Reported-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>