sfc: Distinguish critical and non-critical over-temperature conditions

Set both the 'maximum' and critical temperature limits for LM87
hardware monitors on Falcon boards.  Do not shut down a port until the
critical temperature is reached, but warn as soon as the 'maximum'
temperature is reached.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>