mlxsw: spectrum: PTP: Hook into packet receive path

When configured, the Spectrum hardware can recognize PTP packets and
trap them to the CPU using dedicated traps, PTP0 and PTP1.

One reason to get PTP packets under dedicated traps is to have a
separate policer suitable for the amount of PTP traffic expected when
switch is operated as a boundary clock. For this, add two new trap
groups, MLXSW_REG_HTGT_TRAP_GROUP_SP_PTP0 and _PTP1, and associate the
two PTP traps with these two groups.

In the driver, specifically for Spectrum-1, event PTP packets will need
to be paired up with their timestamps. Those arrive through a different
set of traps, added later in the patch set. To support this future use,
introduce a new PTP op, ptp_receive.

It is possible to configure which PTP messages should be trapped under
which PTP trap. On Spectrum systems, we will use PTP0 for event
packets (which need timestamping), and PTP1 for control packets (which
do not). Thus configure PTP0 trap with a custom callback that defers to
the ptp_receive op.

Additionally, L2 PTP packets are actually trapped through the LLDP trap,
not through any of the PTP traps. So treat the LLDP trap the same way as
the PTP0 trap. Unlike PTP traps, which are currently still disabled,
LLDP trap is active. Correspondingly, have all the implementations of
the ptp_receive op return true, which the handler treats as a signal to
forward the packet immediately.

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>