audio: rename bsd target to netbsd.

Apparently this is no longer a generic BSD audio target, and hasn't been for
years, so rename it for NetBSD.

--HG--
rename : src/audio/bsd/SDL_bsdaudio.c => src/audio/netbsd/SDL_netbsdaudio.c
rename : src/audio/bsd/SDL_bsdaudio.h => src/audio/netbsd/SDL_netbsdaudio.h
10 files changed