platform/wmi: Add kunit test for the marshalling code

platform/wmi: Add kunit test for the marshalling code

The marshalling code used by the WMI driver core is implemented as
a separate component, suitable for unit tests.

Implmented such a unit test using KUnit. Those unit tests verify that
ACPI objects are correctly converted into WMI buffers and that WMI
strings are correctly converted into ACPI strings. They also verify
that invalid ACPI data (like nested packages) is rejected.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://patch.msgid.link/20260116204116.4030-3-W_Armin@gmx.de
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>