ASoC: EP93xx: Add Snapper CL15 i2s audio support

Add support for i2s audio on Bluewater Systems Snapper CL15 module

Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>