Define PARAM so that we have two versions of the "desc_codec
and family" structs. Add a property called "mixer" whose default
value depends on whether CONFIG_MIXEMU is defined or not which
will help us call the appropriate instance init functions.

Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>