tegra: Clarify generation of -nodtb file with OF_CONTROL

Fix the ALL-y logic in the Makefile so that is clear that we always want
the -nodtb file.

Tested-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Simon Glass <sjg@chromium.org>