fm10k: use generic ethtool_op_get_ts_info callback

This generic callback is for drivers which have software Tx timestamp
support enabled. Without this, PTP applications requesting software
timestamps may complain that the requested mode is not supported.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <Krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>