Update to kernel 4.19.81

Added udev rule to allow users to use vcgencmd without sudo (thanks xlazom00)

Fixed udev mounts not being visible (thanks wyuenho for the pull request)

Build script improvements now gets cross chain compiler / qemu user static 4.1 / related build dependencies

Build script now retrieves all dependencies for you on a blank Ubuntu 18.04.3 Virtual Machine (if you want to build)