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

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

[ Upstream commit 9d3f8a723c7950e56e0b95ab84b572caee29e065 ]

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/
Signed-off-by: Sasha Levin <sashal@kernel.org>