hwmon: (mlxreg-fan) Add support for fan drawers capability and present registers

hwmon: (mlxreg-fan) Add support for fan drawers capability and present registers

Add support for fan drawer's capability and present registers in order
to set mapping between the fan drawers and tachometers. Some systems
are equipped with fan drawers with one tachometer inside. Others with
fan drawers with several tachometers inside. Using present register
along with tachometer-to-drawer mapping allows to skip reading missed
tachometers and expose input for them as zero, instead of exposing
fault code returned by hardware.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20210322172237.2213584-1-vadimp@nvidia.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>