iwlwifi: mvm: rs: introduce new API for rate scaling

New devices will have rate scaling algorithm running in the firmware.
With this feature, the driver's responsiblity is to provide an initial
configuration and to handle notifications regarding recent rates and
some other parameters. Debugfs hooks will be still available for
reading the current rate/statistics and setting a fixed rate.
The old API is supported so far, though both APIs cannot be used
simultaneously.

This is the first patch in the series. It adds a new TLV specifying
FW support for the new API and updates lq_sta to support two types
of rate scaling.

Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>