hwmon: (corsair-psu) add reporting of rail mode via debugfs

Add reporting if the PSU is running in single or multi rail mode via
ocpmode debugfs entry. Also update the documentation and driver comments
accordingly.

Signed-off-by: Wilken Gottwalt <wilken.gottwalt@posteo.net>
Link: https://lore.kernel.org/r/YvS9PZKr0xqFqJny@monster.localdomain


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