ALSA: usb: stream: refactor uac1/2 audio interface parsing

Offload snd_usb_parse_audio_interface() function
which became quite long after adding UAC3 spec support.

Move class-specific parts of uac1/2 parsing to separate
function which now produce audioformat structure that
is ready to be fed to snd_usb_add_audio_stream().

This also broke Blue Microphones workaround (which
relies on audioformat decoded from previous altsetting)
into two parts: prepare quirk flag analyzing previous
altsetting then use it with current altsetting.
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>