ASoC: Intel: atom: fix ACPI/PCI Kconfig

The split between ACPI and PCI platforms generated issues with randconfig:

with SND_SST_ATOM_HIFI2_PLATFORM_PCI=y and
SND_SST_ATOM_HIFI2_PLATFORM=m, we get this module link failure:

ERROR: "sst_context_init"
[sound/soc/intel/atom/sst/snd-intel-sst-acpi.ko] undefined!

ERROR: "sst_context_cleanup"
[sound/soc/intel/atom/sst/snd-intel-sst-acpi.ko] undefined!

ERROR: "sst_alloc_drv_context"
[sound/soc/intel/atom/sst/snd-intel-sst-acpi.ko] undefined!

ERROR: "intel_sst_pm" [sound/soc/intel/atom/sst/snd-intel-sst-acpi.ko]
undefined!

ERROR: "sst_configure_runtime_pm"
[sound/soc/intel/atom/sst/snd-intel-sst-acpi.ko] undefined!

To keep things simple, let's expose two configs for
SND_SST_ATOM_HIFI2_PLATFORM_PCI and SND_SST_ATOM_HIFI2_PLATFORM_ACPI,
which select a common SND_SST_ATOM_HIFI2_PLATFORM option. To avoid
breaking existing solutions with the semantics change,
SND_SST_ATOM_HIFI2_PLATFORM_ACPI uses "default ACPI" so that "make
oldnoconfig" and "make olddefconfig" still work as expected.

Also remove mentions of Medfield while we are at it since it was
removed recently.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 4772c16e ("ASoC: Intel: Kconfig: Simplify-clarify ACPI/PCI
dependencies")
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-By: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>