mlxsw: core: Trace EMAD events

Currently, mlxsw triggers the 'devlink:devlink_hwmsg' tracepoint
whenever a request is sent to the device and whenever a response is
received from it. However, the tracepoint is not triggered when an event
(e.g., port up / down) is received from the device.

Also trace EMAD events in order to log a more complete picture of all
the exchanged hardware messages.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>