soundwire: qcom: add support for get_sdw_stream()

Adding support to new get_sdw_stream() that can help machine
driver to deal with soundwire stream.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200317092645.5705-1-srinivas.kandagatla@linaro.org


[fix checkpatch error for "void * qcom_swrm_get_sdw_stream"]
Signed-off-by: Vinod Koul <vkoul@kernel.org>