Add some missing DFS chipset functionality to the FreeBSD HAL.

Please note - this doesn't in any way constitute a full DFS
implementation, it merely adds the relevant capability bits and
radar detection threshold register access.

The particulars:

• Add new capability bits outlining what the DFS capabilities are of the various chipsets.
• Add HAL methods to set and get the radar related register values.
• Add AR5212 and AR5416+ DFS radar related register value routines.
• Add a missing HAL phy error code that's related to radar event processing.
• Add HAL_PHYERR_PARAM, a data type that encapsulates the radar register values.

The AR5212 routines are just for completeness. The AR5416 routines
are a super-set of those; I may later on do a drive-by pass to
tidy up duplicate code.

Obtained from: Linux, Atheros