Add length to write command packet token so that we can track exactly
how many bytes are consumed by DSP in the command reply.

This is useful in some use-cases where the end of the file/stream
is not aligned with period size.
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/20200727093806.17089-5-srinivas.kandagatla@linaro.orgSigned-off-by: Mark Brown <broonie@kernel.org>