hwmon: OCC drivers are ARM-only

These drivers are for a BMC inside PowerPC servers. The BMC runs on
ARM hardware, so only propose the drivers on this architecture, unless
build-testing.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Eddie James <eajames@linux.ibm.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Eddie James <eajames@linux.ibm.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>