atheroswifi: Add AR9300 HAL.

Not really based on KapiX's patch (I looked at his Jamfile changes, but
did the rest of it myself.)

Besides the usual GCC2 (C89) fixes, this commit also changes FreeBSD's code
in removing two of the _reg_map_macro headers and adding only the relevant
portions to a post-preprocessed version of the non _macro files. This spares
us importing 7 MB (!) of headers.

KapiX confirmed his patch as working; hopefully I didn't break anything
in this import.