ASoC: kirkwood: add alias to pcm module

Allow snd-soc-kirkwood autoloading by adding an alias.

Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>