drm/ttm/tests: depend on UML || COMPILE_TEST

At least the device test requires that no other driver using TTM is
loaded. So make those unit tests depend on UML || COMPILE_TEST to
prevent people from trying them on bare metal.
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://lore.kernel.org/all/20240219230116.77b8ad68@yea/

drivers/gpu/drm/Kconfig

@@ -199,7 +199,7 @@ config DRM_TTM
 config DRM_TTM_KUNIT_TEST
         tristate "KUnit tests for TTM" if !KUNIT_ALL_TESTS
         default n
-        depends on DRM && KUNIT && MMU
+        depends on DRM && KUNIT && MMU && (UML || COMPILE_TEST)
         select DRM_TTM
         select DRM_EXPORT_FOR_TESTS if m
         select DRM_KUNIT_TEST_HELPERS
@@ -207,7 +207,8 @@ config DRM_TTM_KUNIT_TEST
         help
           Enables unit tests for TTM, a GPU memory manager subsystem used
           to manage memory buffers. This option is mostly useful for kernel
-          developers.
+          developers. It depends on (UML || COMPILE_TEST) since no other driver
+          which uses TTM can be loaded while running the tests.
 
           If in doubt, say "N".