octeon: remove deprecated syststamp timestamp

Hardware timestamps can be exposed to userspace in raw hardware format
(hwtstamp) as well as converted to system time (syststamp). The second
variant is deprecated and only implemented by this driver.

The preferred method of hardware timestamp generation is to combine
hwtstamp with a device PTP clock. Octeon has its own PTP library
that relies on a shared memory interface to the PTP clock device.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>