axfer: add an option to suppress event waiting

axfer: add an option to suppress event waiting

In aplay, '--test-nowait' is used to suppress calls of snd_pcm_wait()
when I/O operations return -EAGAIN or process truncated number of data
frames. This seems to be for debugging purpose. In this program, this
option is equivalent to suppress event waiting.

This commit adds support for this option.

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