ASoC: cs35l36: Add device tree documentation for CS35L36

Add device tree documentation for Cirrus Logic CS35L36
speaker amplifier

Signed-off-by: James Schulman <james.schulman@cirrus.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Acked-by: Brian Austin <brian.austin@cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>