be2net: Export board temperature using hwmon-sysfs interface.

Ethtool statistics is not the right place to display board temperature.
This patch adds support to export die temperature of devices supported
by be2net driver via the sysfs hwmon interface.

Signed-off-by: Venkat Duvvuru <VenkatKumar.Duvvuru@Emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>