Some work on the wave volume control support
- ES1370: implemented CODEC registers (AK4531 mixer) and wave volume control
- Moved wave volume application code to new method pcm_apply_volume() and use
  it for both soundcards
- TODO: stereo support


git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12026 6c8e4198-a580-4521-a02f-c9ae86df1db9