ASoC: cygnus: Add DT bindings for Broadcom Cygnus audio

Add bindings for audio driver in Broadcom Cygnus.

Signed-off-by: Lori Hikichi <lhikichi@broadcom.com>
Signed-off-by: Simran Rai <ssimran@broadcom.com>
Reviewed-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>