software node: add basic tests for property entries

This adds tests for creating software nodes with properties supplied by
PROPERTY_ENTRY_XXX() macros and fetching and validating data from said
nodes/properties.

We are using KUnit framework for the tests.
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/test/Makefile

 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_TEST_ASYNC_DRIVER_PROBE)	+= test_async_driver_probe.o
+
+obj-$(CONFIG_KUNIT) += property-entry-test.o