drm: Ensure universal_planes is set for atomic

Atomic doesn't really work without universal planes anyway. But make
sure that evil userspace doesn't pull the kernel over the table
because we didn't consider a cornercase that just doesn't make sense,
just for safety.

v2: Just force ->universal_planes to the same value to avoid imposing
restrictions on userspace.

Cc: Rob Clark <robdclark@gmail.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>