This commit adds common PCM constraints according to current firewire-lib
implementation.

1.Maximum width for each sample is limited by 24.
AM824 in IEC 61883-6 can deliver 24bit data.

2. Minimum time for period is 5msec.
Apply the old value. For shorter latency, further works are needed.

3. In blocking mode, frames per period/buffer is aligned to 32.
Each packet can include some frames depending on its sampling rate. In
blocking mode, the number equals to SYT_INTERVAL. Currently firewire-lib
can schedule snd_pcm_period_elapsed() for each packet. So, for accurate
PCM interrupt, the number of frames per period/buffer should be aligned
to SYT_INTERVAL.
Currently firewire-lib is lack of better rules to achieve this. So LCM of
each value of SYT_INTERVALs (=32) is applied. This can be improved for
further work.

[Fixed the compile error due to the missing "&" by tiwai]

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