ASoC: Intel: improve SND_SOC_INTEL_MACH dependencies

I ran into a build error with CONFIG_SND_SOC_INTEL_COMMON=m
and SND_SOC_INTEL_MACH=y:

ERROR: "snd_soc_acpi_intel_broadwell_machines" [sound/soc/intel/common/snd-soc-sst-acpi.ko] undefined!
ERROR: "snd_soc_acpi_intel_haswell_machines" [sound/soc/intel/common/snd-soc-sst-acpi.ko] undefined!
ERROR: "snd_soc_acpi_intel_cherrytrail_machines" [sound/soc/intel/atom/sst/snd-intel-sst-acpi.ko] undefined!
ERROR: "snd_soc_acpi_intel_baytrail_machines" [sound/soc/intel/atom/sst/snd-intel-sst-acpi.ko] undefined!

The problem here is that the sound/soc/intel/common/ directory
is then entered only for building modules, but the sst-acpi.o
never gets built since it depends on a built-in Kconfig symbol.

That configuration obviously makes no sense since all options
below SND_SOC_INTEL_MACH also depend on something else that
in turn depends on CONFIG_SND_SOC_INTEL_COMMON.

Adding a SND_SOC_INTEL_SST_TOPLEVEL dependency to SND_SOC_INTEL_MACH
solves the build error. I notice we can also consolidate the
'depends on SND_SOC_INTEL_MACH' lines by using an 'if' block to
simplify it further and make sure the configuration stays sane.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-By: Vinod Koul <vinod.koul@intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>