net: ethernet: altera: Add use of ethtool_op_get_ts_info

Add the ethtool_op_get_ts_info() callback to ethtool ops, so that we can
at least use software timestamping.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://lore.kernel.org/r/20220817095725.97444-1-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>