axfer: add support for a mapper for single target

axfer: add support for a mapper for single target

In usual use case of aplay, single file is used to playback or capture data
frames.

This commit adds support of single type mapper for this use case. All of
supported file format can include data frame with interleaved alignment,
thus this mapper have a functionality to convert from several types of
data frame alignment to interleaved alignment or vise versa. When
handling non-interleaved buffer, a caller should use an array of buffer
for each of channels with non-interleaved data frames.

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