ASoC: add component_list_show()

commit ef050bec ("ASoC: Remove platform code now everything is
componentised") removed platform code, then platform_list_show() was
removed, too. But we want to keep it as component_list_show.
This patch add it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>