hwmon: (occ) Add sysfs entry for OCC mode

BMC control applications need to check the OCC mode returned by the
OCC poll response, so export it in sysfs with the other OCC-specific
data.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20220215151022.7498-3-eajames@linux.ibm.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>