dt-bindings: hwmon: Document ibm,cffps compatible string

Document this string that indicates that any version of the power supply
may be connected. In this case, the driver must detect the version
automatically.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1570648262-25383-2-git-send-email-eajames@linux.ibm.com


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