Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

[athspectral] add a knob to expose the spectral scan priority.

This is required for AR9380 and later chips.. please leave it at 0 for now.

Remove the hard-coded 'ath0' strings and use ATH_DEFAULT.

Remove the duplicate ATH_DEFAULT fields. The build bits should be including
../Makefile.inc as appropriate.

Add missing formatting strings.

Thanks to: clang

Add the "enable at reset" functionality to trigger spectral scan upon
a channel change/reset.

Add a very skeletal spectral scan control application.

The main use for this is to manually trigger spectral scan operations
(athspectral -i athX start) whilst doing debugging.