linuxPackages.bbswitch: disable on AArch64

It makes no sense on non-x86 platforms.

pkgs/os-specific/linux/bbswitch/default.nix

···
 
   meta = with stdenv.lib; {
     description = "A module for powering off hybrid GPUs";
-    platforms = platforms.linux;
+    platforms = [ "x86_64-linux" "i686-linux" ];
     homepage = https://github.com/Bumblebee-Project/bbswitch;
     maintainers = with maintainers; [ abbradar ];
   };