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

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

[ath] migrate ioctl and busdma memory operations out into separate source files.

This should be a big no-op pass; and reduces the size of if_ath.c.

I'm hopefully soon going to take a whack at the USB support for ath(4)
and this'll require some reuse of the busdma memory code.