Linux 4.x kernel notes

Starting with the 4.4 kernel, NVIDIA maintains separate repositories for some of their hardware-specific drivers and the device tree files. To simplify kernel builds under OE-Core, the linux-tegra recipes for 4.4 and later point to a repository where the files in those separate repositories have been merged back together using git subtrees.

This makes it more difficult to compare the sources used here against the NVIDIA upstream sources, but simplifies the recipe and the management any patches that might be needed.