mlxsw: Support CQEv2 for SDQ in Spectrum-2 and newer ASICs

Currently, Tx completions are reported using Completion Queue Element
version 1 (CQEv1). These elements do not contain the Tx time stamp,
which is fine as Spectrum-1 reads Tx time stamps via a dedicated FIFO
and Spectrum-2 does not currently support PTP.

In preparation for Spectrum-2 PTP support, use CQEv2 for Spectrum-2 and
newer ASICs, as this CQE format encodes the Tx time stamp.

Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>