mlxsw: spectrum: PTP: Support timestamping on Spectrum-1

On Spectrum-1, timestamps arrive through a pair of dedicated events:
MLXSW_TRAP_ID_PTP_ING_FIFO and _EGR_FIFO. The payload delivered with
those traps is contents of the timestamp FIFO at a given port in a given
direction. Add a Spectrum-1-specific handler for these two events which
decodes the timestamps and forwards them to the PTP module.

Add a function that parses a packet, dispatching to ptp_classify_raw(),
and decodes PTP message type, domain number, and sequence ID. Add a new
mlxsw dependency on the PTP classifier.

Add helpers that can store and retrieve unmatched timestamps and SKBs to
the hash table added in a preceding patch.

Add the matching code itself: upon arrival of a timestamp or a packet,
look up the corresponding unmatched entry, and match it up. If there is
none, add a new unmatched entry. This logic is the same on ingress as on
egress.

Packets and timestamps that never matched need to be eventually disposed
of. A garbage collector added in a follow-up patch will take care of
that. Since currently all this code is turned off, no crud will
accumulate in the hash table.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>