ASoC: kirkwood: Add i2s support

This patch enables support for the i2s controller available on kirkwood
platforms

Signed-off-by: Arnaud Patard <apatard@mandriva.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>