To accomodate the raccoon knights workstation, some of the configuration
pulled by m/common/main.nix has to be removed. To solve it, the xeon
specific parts are placed into m/common/xeon.nix and only the common
configuration is at m/common/base.nix.
Reviewed-by: Aleix Roca Nonell <aleix.rocanonell@bsc.es>
