audio: move & rename soundhw init code.

# gpg: Signature made Fri 19 May 2017 12:22:51 PM BST
# gpg:                using RSA key 0x4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* kraxel/tags/pull-audio-20170519-1:
  audio: Rename hw/audio/audio.h to hw/audio/soundhw.h
  audio: Rename audio_init() to soundhw_init()
  audio: Move arch_init audio code to hw/audio/soundhw.c

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>