/arm64/boot/dts

In the l4t kernel source code, in the kernel-4.9/arch/arm64/boot/dts/Makefile file, why does dts-dirs have no description about nvidia, as shown in the following figure

In the kernel-4.9/arch/arm64/boot/dts/nvidia directory, why is there no TX2-related device tree file, tegra186*, as shown in the following figure

thank you !!