ALSA: pxa2xx-ac97-lib: support building for several CPUs

Support building of pxa2xx-ac97-lib for several CPUs by making code
run-time selected, not only compile-time.

[Fixed 3XX->3xx typos in ifdef checks -- broonie.]

Signed-off-by: Dmitry Baryshkov <dbaryshkov@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>