audio: add Apple Sound Chip (ASC) emulation

audio: add Apple Sound Chip (ASC) emulation

The Apple Sound Chip was primarily used by the Macintosh II to generate sound
in hardware which was previously handled by the toolbox ROM with software
interrupts.

Implement both the standard ASC and also the enhanced ASC (EASC) functionality
which is used in the Quadra 800.

Note that whilst real ASC hardware uses AUDIO_FORMAT_S8, this implementation uses
AUDIO_FORMAT_U8 instead because AUDIO_FORMAT_S8 is rarely used and not supported
by some audio backends like PulseAudio and DirectSound when played directly with
-audiodev out.mixing-engine=off.

Co-developed-by: Laurent Vivier <laurent@vivier.eu>
Co-developed-by: Volker Rümelin <vr_qemu@t-online.de>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-ID: <20231004083806.757242-8-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>