axfer: add support for a container of raw data

axfer: add support for a container of raw data

This commit adds support for raw data without any headers/chunks/blocks.
A parser of container cannot recognize format of sample without
supplemental information.

Additionally, it includes no magic bytes. A parser of container should
process first several bytes as a part of PCM frames, instead of magic
bytes.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>