ASoC: pxa: remove bindings from pxa2xx-pcm

This platform is no longer needed on DT boards, so let's remove them to
avoid confusion. DT bindings should use the CPU DAIs (I2S/SSP/AC97)
directly.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Mark Brown <broonie@kernel.org>