ASoC: samsung: Document DT bindings for Midas sound subsystem

This patch adds documentation of DT biding for the Midas sound complex.
Partially based on the *txt version by Simon Shields <simon@lineageos.org>.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200728131111.14334-1-s.nawrocki@samsung.com


Signed-off-by: Mark Brown <broonie@kernel.org>