The capture stream of BOSS GT-001 seems always requiring to be tied
with the playback stream.  OTOH, the playback stream of this device
doesn't seem working in the implicit fb mode, per se, since the
playback must be running before the capture stream.

This patch tries to address the points above:
- Avoid the implicit fb mode for the playback
- Set up a fake sync EP for the capture stream with the hard-coded
  playback stream using the implicit fb mode
Reported-by: Keith Milner <kamilner@superlative.org>
Tested-by: Keith Milner <kamilner@superlative.org>
Tested-by: Dylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-37-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>