ASoC: Remove adau1701 from SND_SOC_ALL_CODECS due to Sigma dependency

The Sigma code is in drivers/firmware which is only included on a very
small subset of architectures and so ends up breaking the build on
others.  There's a pending patch to make the directory build as standard
but it's not merged yet.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>