mlxsw: core: Extend hwmon interface with fan fault attribute

Add new fan hwmon attribute for exposing fan faults (fault indication is
read from Fan Out of Range Event Register).

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>