bnxt_en: improve fw diagnose devlink health messages

Add firmware event counters as well as health state severity. In
the unhealthy state, recommend a remedy and inform the user as to
its impact.

Readability of the devlink tool's output is negatively impacted by
adding these fields to the diagnosis. The single line of text, as
rendered by devlink health diagnose, benefits from more terse
descriptions, which can be substituted without loss of clarity, even
in pretty printed JSON mode.

Signed-off-by: Edwin Peer <edwin.peer@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>