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

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

bwn(4): migrate bwn(4) to the native bhnd(9) interface, and drop siba_bwn.

- Remove the shim interface that allowed bwn(4) to use either siba_bwn or
bhnd(4), replacing all siba_bwn calls with their bhnd(4) bus equivalents.
- Drop the legay, now-unused siba_bwn bus driver.
- Clean up bhnd(4) board flag defines referenced by bwn(4).

Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D13518

[bwn] begin migrating PHY common routines into if_bwn_phy_common.[ch].

This isn't compiled in yet; so some code here duplicates what
is in the existing code. I'll migrate it all out in subsequent
commits.

Obtained from: b43 (definitions), bcm-v4 specifications website