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

Add support for fan capability registers in order to distinct between
the systems which have minor fan configuration differences. This
reduces the amount of code used to describe such systems.
The capability registers provides system specific information about the
number of physically connected tachometers and system specific fan
speed scale parameter.
For example one system can be equipped with twelve fan tachometers,
while the other with for example, eight or six. Or one system should
use default fan speed divider value, while the other has a scale
parameter defined in hardware, which should be used for divider
setting.
Reading this information from the capability registers allows to use the
same fan structure for the systems with the such differences.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>