[Backport release-22.05] arm-trusted-firmware: unfree only if hdcp.bin used

[ghost]

This is a cherry-pick of 8485bfc which was merged from issue #174691.

This commit reduces the scope of a breaking change relative to 21.11.

Specifically, it allows the arm-trusted-firmware for non-Rockchip devices to be built without NIXPKGS_ALLOW_NONFREE=1, as was possible in 21.11.

Description of changes

The unfreeIncludeHDCPBlob parameter was introduced as a result of
this reviewer request:

#148890 (comment)

The default value unfreeIncludeHDCPBlob?true causes a change in the
meta.license field for all of the subpackages within
pkgs/misc/arm-trusted-firmware/, and results in them needing
NIXPKGS_ALLOW_NONFREE=1.

For non-Rockchip platforms the file hdcp.bin does not get included in
the output; the blob is for a Synopsys HDCP core that is currently
used only by Rockchip (although other companies could license it from
Synopsys in the future). Therefore on non-Rockchip we can delete
hdcp.bin before building instead of changing the license. This
preserves the ability to build them without NIXPKGS_ALLOW_NONFREE=1.

Let's do that.

Deleting hdcp.bin ensures that we won't be caught by surprise if some
future non-Rockchip Arm CPU licenses the same Synopsys HDCP core that
Rockchip is using.

Use easier-to-follow names for controlling the blob
inclusion/exclusion. Also, if the blob is believed to be unnecessary,
delete it beforehand so we will know if we were wrong about that belief.

Co-authored-by: Sandro sandro.jaeckel@gmail.com
(cherry picked from commit 8485bfc)

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.11 Release Notes (or backporting 22.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.