ASoC: arm: make pxa2xx-ac97-lib ac97 codec agnostic

All pxa library functions don't use the input parameters for nothing but
slot number. This simplifies their prototypes, and makes them usable by
both the legacy ac97 bus and the new ac97 bus.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>