ASoC: Intel: use CONFIG_SND_SOC for intel boards

The Intel boards directory was under CONFIG_SND_SOC_INTEL_SST so the
machines which don't need these were not allowed to be
selected/compiled without enabling this symbol The machine should be
allowed to selected by ASoC and then they should select rest of
symbols required

Reported-by: Michele Curti <michele.curti@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Acked-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>