hwmon: (mlxreg-fan) Add support for Mellanox FAN driver

Driver obtains PWM and tachometers registers location according to the
system configuration and creates FAN/PWM hwmon objects and a cooling
device. PWM and tachometers are controlled through the on-board
programmable device, which exports its register map. This device could be
attached to any bus type, for which register mapping is supported. Single
instance is created with one PWM control, up to 12 tachometers and one
cooling device. It could be as many instances as programmable device
supports.

Currently driver will be activated from the Mellanox platform driver:
drivers/platform/x86/mlx-platform.c.
For the future ARM based systems it could be activated from the ARM
platform module.

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