ALSA: firewire-motu: add ioctl command to read cached parameters in register DSP model

This patch adds new ioctl command for userspace applications to read
cached parameters of register DSP.

The structured data includes model-dependent parameters. Userspace
application should be carefully programmed so that what parameter is
common and specific.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20211015080826.34847-10-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Iwai <tiwai@suse.de>