audio: Move arch_init audio code to hw/audio/soundhw.c

There's no reason to keep the soundhw table in arch_init.c. Move
that code to a new hw/audio/soundhw.c file.

While moving the code, trivial coding style issues were fixed.

Signed-off-by: Eduardo Habkost <[email protected]>
Reviewed-by: David Gibson <[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-id: 20170508205735[email protected]
Signed-off-by: Gerd Hoffmann <[email protected]>