nvidia jetson NANO platform交叉编译

1. WIKI: https://forums.developer.nvidia.com/t/links-to-jetson-nano-resources-wiki/71639

2. 下载L4T(Linux for Tegra) Driver Package (BSP) Sources，GCC工具链

　　https://developer.nvidia.com/embedded/linux-tegra

3. 解压工具链gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu.tar.xz

4. 环境变量export

　　export CROSS_COMPILE_AARCH64_PATH=/opt/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu

　　export NV_TARGET_BOARD=t210ref

5. 执行脚本编译kernel和uboot：cd source/public && ./nv_public_src_build.sh