Synthesized speaker device

[Nathanial Sloss <nat%netbsd.org@localhost>]

Hi,

I have a keyboard bell spkr(4) device to be used with nextaudio5-kern.diff.gz.

It is located in ftp://ftp.netbsd.org/pub/NetBSD/misc/nat/spkr.diff.gz

It is usefull on platforms without a keyboard bell and / or a PCPPI speaker 
interface.

If there are no objections, I'd like to commit this after the audio mixing 
changes.

Best regards,

Nat