Split xeon specific configuration from base

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>

m/common/base/env.nix

@@ -0,0 +1,35 @@
+{ pkgs, config, ... }:
+
+{
+  environment.systemPackages = with pkgs; [
+    vim wget git htop tmux pciutils tcpdump ripgrep nix-index nixos-option
+    nix-diff ipmitool freeipmi ethtool lm_sensors ix cmake gnumake file tree
+    ncdu config.boot.kernelPackages.perf ldns
+    # From bsckgs overlay
+    osumb
+  ];
+
+  programs.direnv.enable = true;
+
+  # Increase limits
+  security.pam.loginLimits = [
+    {
+      domain = "*";
+      type = "-";
+      item = "memlock";
+      value = "1048576"; # 1 GiB of mem locked
+    }
+  ];
+
+  environment.variables = {
+    EDITOR = "vim";
+    VISUAL = "vim";
+  };
+
+  programs.bash.promptInit = ''
+    PS1="\h\\$ "
+  '';
+
+  time.timeZone = "Europe/Madrid";
+  i18n.defaultLocale = "en_DK.UTF-8";
+}