platform/x86: mlx-platform: Extend FAN platform data description

Extend FAN platform data with register presence field.
Add register present entry per rotor (tachometer) description tuple.
The purpose is to allow indication of FAN presence.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>