ALSA: firewire-lib: add list of packet descriptor

In current implementation of ALSA IEC 61883-1/6 packet streaming engine,
16 packets are handled in one interrupt of isochronous context of OHCI
1394.

Overall packet processing runs for each. However, this is not better in
a point to split the processing into several parts.

This commit is an attempt to add intermediate representation for
parameters required for the parts.

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