ASoC: qcom: common: Support parsing links without DPCM

ASoC: qcom: common: Support parsing links without DPCM

So far qcom_snd_parse_of() was only used to parse the device tree
for boards using the QDSP6 driver together with DPCM. apq8016_sbc
uses an almost identical version (apq8016_sbc_parse_of()) which
parses links without DPCM.

Given the similarity of the two functions it is useful to combine
these two. To allow using qcom_snd_parse_of() in apq8016_sbc we
need to support parsing links without DPCM as well.

This is pretty simple: A DPCM link in the device tree is defined using:

  - DPCM frontend: "cpu"
  - DPCM backend:  "cpu", "platform" and "codec"

... while a link without DPCM has "cpu" and "codec" (but no "platform").

Add a few more if conditions to handle links without DPCM correctly.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Tested-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200723183904.321040-5-stephan@gerhold.net
Signed-off-by: Mark Brown <broonie@kernel.org>