import https://nixos.org/wiki/Raspberry_Pi_2

Fixes https://github.com/NixOS/nixpkgs/issues/13175

raspberry_pi/rpi2.nix

@@ -0,0 +1,58 @@
+/** imported from https://nixos.org/wiki/Raspberry_Pi_2 **
+
+# Status
+The code in master as of June 2015 should be able to prepare a bootable NixOS for Raspberry PI 2.
+
+There are still some drawbacks:
+
+NixOS does not provide a /boot/config.txt (the FAT32 partition).
+Making NixOS work in the Raspberry PI 2 is mainly the result of the recent work of ambro718, Dezgeg and viric (#nixos@irc.freenode.net).
+
+# Download
+If you want to test, you can flash this 4GB SD image (DOS partition table + fat32 + ext4 rootfs):
+magnet:?xt=urn:btih:0def3f6acb3bceddb22cb24098f58e40e2853ec2&dn=rpi2-nixos-4b09501f2-img.xz&tr=udp%3A%2F%2Fopen.demonii.com%3A1337&tr=udp%3A%2F%2Ftracker.openbittorrent.com%3A80
+
+Then you should be able to nixos-rebuild any configuration.nix changes.
+
+The image is the result of a "nixos-install" alone. No root password has been set, and it does not include a nixpkgs checkout or channel.
+
+In fact I (viric) created the FS into a NBD, not a real SD, to create this image.
+
+*/
+
+{pkgs, config, ...}:
+
+{
+  boot.consoleLogLevel = 7;
+  boot.loader.grub.enable = false;
+  boot.loader.generationsDir.enable = false;
+  boot.loader.raspberryPi.enable = true;
+  boot.loader.raspberryPi.version = 2;
+  boot.extraTTYs = [ "ttyAMA0" ];
+  boot.kernelPackages = pkgs.linuxPackages_rpi;
+  boot.kernelParams = [
+    #"coherent_pool=6M"
+    #"smsc95xx.turbo_mode=N"
+    "dwc_otg.lpm_enable=0"
+    "console=ttyAMA0,115200"
+    "rootwait"
+    #"console=tty1"
+    "elevator=deadline"
+  ];
+
+  # cpufrequtils doesn't build on ARM
+  powerManagement.enable = false;
+
+  services.xserver.enable = false;
+  services.openssh.enable = true;
+
+  services.nixosManual.enable = false;
+
+  nixpkgs.config = {
+    platform = pkgs.platforms.raspberrypi2;
+    allowUnfree = true;
+  };
+
+  nix.buildCores = 4;
+  nix.binaryCaches = [ ];
+}