ALSA: usb-audio: Add generic implicit fb parsing

This patch extends the implicit feedback mode parser code to check the
description more generically, so that the quirk entries can be added
without the explicit EP and interface numbers.  The search is done for
the next and the previous interface of the given altset, and if both
entries are ASYNC mode and the direction matches, it just takes as the
sync endpoint.  The generic parser is applicable only for the playback
stream.

As of now, only a few M-Audio devices have been converted to use this
mode.

Tested-by: Keith Milner <kamilner@superlative.org>
Tested-by: Dylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-39-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>