drm/amd/display: Introduce KUnit tests to the display_mode_vba library

The display_mode_vba library deals with hundreds of display parameters
and sometimes does it in odd ways. The addition of unit tests intends to
assure the quality of the code delivered by HW engineers and, also make
it possible to refactor the code decreasing concerns about adding bugs
to the codebase.

Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Co-developed-by: Tales Aparecida <tales.aparecida@gmail.com>
Signed-off-by: Tales Aparecida <tales.aparecida@gmail.com>