ASoC: Remove platform code now everything is componentised

As all drivers have been moved over to the new generic component
code remove the now unused platform specific code.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Acked-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>