ASoC: Intel: remove redundant select SND_SOC_INTEL_SST

SND_SOC_INTEL_SKYLAKE selects SND_SOC_INTEL_SST already. Thus no need to
duplicate. Remove duplications.

Acked-by: Vinod Koul <vinod.koul@intel.com>
Acked-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>