raspberrypi-armstubs: run pre/post hooks in installPhase

pkgs/os-specific/linux/firmware/raspberrypi/armstubs.nix

···
   ;
 
   installPhase = ''
+    runHook preInstall
     mkdir -vp $out/
     cp -v *.bin $out/
+    runHook postInstall
   '';
 
   meta = with lib; {