sys: Remove $FreeBSD$: two-line .h pattern

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

[bwn] add Q52 macros.

The PHY-N code uses a different format for gain values, so these macros
are used for converting to/from and print out values.

[bwn] migrate sqrt and add another couple of util routines.

bwn_sqrt() is in the PHY-LP code but is also needed by the upcoming
PHY-N support.

The other two routines are used by the PHY-N code.

The next commit will introduce it into the compile and pull bwn_sqrt()
out of the PHY-LP source.