LF-3665-4 ASoC: SOF: Introduce fragment elapsed notification API

LF-3665-4 ASoC: SOF: Introduce fragment elapsed notification API

After each fragment is accepted by the DSP we need to inform
the userspace applications that they can send the next fragment.
This is done via snd_compr_fragment_elapsed.

Similar with the PCM case, in order to avoid sending an IPC before
the previous IPC is handled we need to schedule a delayed work to
call snd_compr_fragment_elapsed().

See snd_sof_pcm_period_elapsed.

To sum up this patch offers the following API to SOF code:
	* snd_sof_compr_init_elapsed_work
	* snd_sof_compr_fragment_elapsed

Note that implementation for compressed function is in a new file
selected via CONFIG_SND_SOC_SOF_COMPRESS config option.

For symmetry we introduce snd_sof_pcm_init_elapsed_work to setup
the work struct for PCM case.

Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>