arm-trusted-firmware: add unfreeIncludeHDCPBlob?true to control license and blob-removal patch
arm-trusted-firmware: add unfreeIncludeHDCPBlob?true to control license and blob-removal patch

This change implements @lukegb's idea:

  https://github.gitop.top/NixOS/nixpkgs/issues/148890#issuecomment-1032002903

Specifically, it introduces a new parameter unfreeIncludeHDCPBlob
(defaults to true):

* If unfreeIncludeHDCPBlob==true then the license is changed to
  unfreeRedistributable, which will alert the user to the fact that
  the blob is being included (unless they set NIXPKGS_ALLOW_UNFREE=1).

* If unfreeIncludeHDCPBlob==false then the license is kept as bsd3, but
  a patch is applied to remove the HDCP blob from the build.

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