hpuefi: only build on x86_64

pkgs/os-specific/linux/hpuefi-mod/default.nix

···
     homepage = "https://ftp.hp.com/pub/caps-softpaq/cmit/linuxtools/HP_LinuxTools.html";
     description = "Kernel module for managing BIOS settings and updating BIOS firmware on supported HP computers";
     license = lib.licenses.gpl2Only; # See "License" section in ./non-rpms/hpuefi-mod-*.tgz/README
-    platforms = lib.platforms.linux;
+    platforms = [ "x86_64-linux" ];
     maintainers = with lib.maintainers; [ tomodachi94 ];
   };
 })