Add support to gapless playback by implementing metadata,
next_track, drain and partial drain support.

Gapless on Q6ASM is implemented by opening 2 streams in a single
q6asm stream and toggling them on next track.
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Tested-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/20200727093806.17089-10-srinivas.kandagatla@linaro.orgSigned-off-by: Mark Brown <broonie@kernel.org>