afh_common.c: Avoid ifdefs.

afh_common.c: Avoid ifdefs.

For each optional audio format we currently have two #ifdefs in
afh_common.c: the first one controls whether cpp emits the declaration
of the corresponding init function of the audio format handler while
the second #ifdef prevents the ->init pointer from being initialized
for unsupported audio formats.

Declaring also those init functions which end up as undefined symbols
causes no problems because we never refer to them due to the second set
of #ifdefs.

Hence let's just get rid of the first set of #ifdefs and declare all
xxx_init() functions unconditionally.