ASoC: Initial WM8958 audio configuration

The WM8958 is a WM8994 derivative. This patch merely ensures that some
revision specific configuration for WM8994 is not enabled on WM8994,
additional patches will add support for the new features introduced on
the WM8958.

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