ASoC: topology: KUnit: Add KUnit tests passing empty topology with variants to snd_so...

ASoC: topology: KUnit: Add KUnit tests passing empty topology with variants to snd_soc_tplg_component_load

In order to ensure correct behaviour of topology API, add unit tests
exercising topology functionality.

Add "empty" topology template and tests for parsing it. Also adds few
variants with bad magic numbers.

Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Tested-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210120152846.1703655-5-amadeuszx.slawinski@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>