docker: fix dependencies and broken links
Created by: leandro-arm
This patch fixes all outdated dependencies and broken links.
ArmClang compiler 6 is not longer provided in the Docker image, if it is required the compiler directory should be mounted as a volumen in the specified location in the documentation.
LLVM was updated to the latest supported version by the firmware with the instalation script that build the compiler-rt assets.
For the dev
taget an user was created following the recomendations from Docker documentation.
Change-Id: I28bc940fefa754796e98f473bdb1f85bd13cc683