ASoC: cygnus: Add Cygnus audio DMA driver

This patch adds Cygnus audio DMA driver. It supports playback
and capture modes and uses ringbuffers for data transfer.

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: Arun Parameswaran <arunp@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Mark Brown <broonie@kernel.org>