Even when eventually building u-boot-dtb-tegra.bin, separately building
u-boot-nodtb-tegra.bin can be useful, since building it encapsulates the
SPL padding step. If you want to tweak u-boot.dtb and regenerate
u-boot-dtb-tegra.bin, it is then a simple cat operation.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>