Add toradex apalis imx6 board configs

[deadloko]

Greetings, this config's is working on my custom board. I was able to successfully build minimal image and boot into a root shell.

One thing I wonder though - minimal image is 2.2gb size, but there is no multimedia, heavy frameworks or x server, similar yocto images is only 100-200 mb size. Also, there are some x86 libraries that taking up some space:

[root@nixos-on-arm:~]# file /nix/store/k4mdai2d2qa5fdq2fflzan9ic6m43dz9-gcc-7.4.0/bin/gcc
/nix/store/k4mdai2d2qa5fdq2fflzan9ic6m43dz9-gcc-7.4.0/bin/gcc: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /nix/store/64wbvpm20in97sxgx6pfy6xy5d56fa8m-glibc-2.27/lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, stripped

[root@nixos-on-arm:~]# du -sh /nix/store/k4mdai2d2qa5fdq2fflzan9ic6m43dz9-gcc-7.4
130M	/nix/store/k4mdai2d2qa5fdq2fflzan9ic6m43dz9-gcc-7.4.0/

[deadloko]

Unfortunately it won't build in travis, cause there is no cache in cachix, build causes full rebuild (cause of different cpu) and travis limit for entire job is 50m.

[illegalprime]

🎉
thank you @deadloko ! this board is pretty sweet. just saw thus so I'll review this PR tomorrow

[illegalprime]

re: size: yeah, recently @delroth and I did some work on removing x86 taint:
NixOS/nixpkgs#58606
NixOS/nixpkgs#59787

which brought the image size down to 1.5GB, we need to do more stripping:
NixOS/nixpkgs#21667 (comment)
NixOS/nixpkgs#15339

and finally the last remnants of x86 (build time contamination) should be eliminated by fixing patchShebangs:
NixOS/nixpkgs#33956
NixOS/nixpkgs#43833

the first gcc changes are included in the next branch, and I've been starting to track all the x86 contaminants of images in this file:
https://github.com/illegalprime/nixos-on-arm/blob/next/taint

so there's a lot of work to be done in decreasing size, apart from the above one could also try to disable things that NixOS installs by default, disable dependencies of some packages, etc.

hope that clears things up!

[illegalprime]

code looks good, it's building on my machine so i'll approve when it finishes

[illegalprime]

@deadloko if it still matters to you I got the image size down in master to 566MB
https://github.com/illegalprime/nixos-on-arm#a-note-on-image-size
there's still a lot of room to shrink the image, but it's a start.

[deadloko]

@illegalprime It's good to know, now i may test and see if i can use nixos in production.