hwmon: (mlxreg-fan) Extend driver to support multiply PWM

Add additional PWM attributes in order to support the systems, which
can be equipped with up-to four PWM controllers. System capability of
additional PWM support is validated through the reading of relevant
registers.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20210916194719.871413-3-vadimp@nvidia.com


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