Add ODroid M1

[joshbuker]

Based on @KhashayarDanesh's work in #1269, which is also based on the work of @sstent and @povik.

Closes #1269

Description of changes

Continues the work of previous users in adding NixOS support for the ODroid M1.

• Updated substituteAll to use replaceVarsWith per deprecation warnings.
• Updated note at top of kboot.conf to mention that the file is auto-generated
• Cleaned up the path setting in the generate-kboot-conf.sh script
• Fixed the script using sh instead of bash as the interpreter

Things done

• Tested the changes in your own NixOS Configuration
• Tested the changes end-to-end by using your fork of nixos-hardware and
  importing it via <nixos-hardware> or Flake input

I still need to make a few more tweaks (e.g. set sdImage.populateRootCommands when generating the initial .img, which is critical for the boot sequence), but opening the draft for review. @Mic92

[joshbuker]

See also: https://github.com/joshbuker/nixos-on-odroid-m1

[joshbuker]

Weird issue I'm running into - the UUID for the ext4 partition is 44444444-4444-4444-8888-888888888888... Only other issue I've found that may be related is: NixOS/nixpkgs#473135

[joshbuker]

Tested and confirmed fully functional on multiple ODroid M1's. I tested both the sd image / flashing to an NVMe drive, as well as rebuilding the system via nixos-rebuild switch.

Turns out the disabling of grub is required, but the kernel and filesystem stuff is no longer relevant (appears to build just fine without both). When I ran nixos-generate-config it only returned nvme as an available module, so I slimmed that down and it appears to still be booting/loading just fine.

[joshbuker]

@Mic92 This is now ready for review/merging, when you have time.