Add compress interface to SOF

[dbaluta]

This will allow playback of compressed files using SOF. This is still work in progress but I wanted to send the patches for early review to understand if I'm following a correct direction.

First 4 patches can be separately be merged and they are needed to make space for introducing the compress interface. There are a lot of similarities between compr and PCM and will try to make a common abstraction when possible.

With current patches I'm able to use compress interface to play PCM samples using dummy codec from SOF.

cplay -v -c 3 -d 0 -I PCM -b 65536 -f 2 sample.wav

First step in trying to unify PCM / compr handling is adding snd_compr_stream filed to snd_sof_pcm_stream:

--- a/sound/soc/sof/sof-audio.h
+++ b/sound/soc/sof/sof-audio.h
@@ -34,6 +34,7 @@ struct snd_sof_pcm_stream {
        struct snd_pcm_substream *substream;
+       struct snd_compr_stream *cstream;

Next is having a common snd_sof_period_elapsed function for both PCM / compr.

Looking at snd_compress_ops and sof_pcm* there are some common part (with particular stress on sof_pcm_hw_params and sof_compr_set_params but I preferred for now to keep the changes separate (even if there is some duplicate code).

Please have a look and let me know what you think at first glance. More patches will come in the next days as I'm trying to support a real codec.

Cc: @paulstelian97 @iuliana-prodan @TE-N-ShengjiuWang