ALSA: speakers: Rename to oxfw and rename some members

This commit renames 'firewire-speakers' to 'oxfw' to enhance support for
devices which based on OXFW970/971. A line for MODULE_ALIAS is added.

Additionally, to help for works in followed paches, some members
in private structure are renamed.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>