linuxPackages.framework-laptop-kmod: install module through modules_install

Installing the module by hand bypasses Kbuild's module installation
flow, which since #571181 is what signs each module with kmodigest and
installs its per-module certificate. The package therefore only
produced `framework_laptop.ko`, and building `system.modulesTree`
failed while concatenating the certificates of external modules:

    cat: extra/framework_laptop.ko.cer: No such file or directory

Install via `modules_install` so the module is signed and its
certificate is installed alongside it, matching the other kernel
module packages fixed in this way.

See #575192.

pkgs/os-specific/linux/framework-laptop-kmod/default.nix

@@ -22,13 +22,12 @@ stdenv.mkDerivation {
 
   makeFlags = kernelModuleMakeFlags ++ [
     "KDIR=${kernel.dev}/lib/modules/${kernel.modDirVersion}/build"
+    "INSTALL_MOD_PATH=${placeholder "out"}"
+    "INSTALL_MOD_DIR=extra"
+    "DEPMOD=true"
   ];
 
-  installPhase = ''
-    runHook preInstall
-    install -D framework_laptop.ko -t $out/lib/modules/${kernel.modDirVersion}/extra
-    runHook postInstall
-  '';
+  installTargets = [ "modules_install" ];
 
   passthru.updateScript = unstableGitUpdater { };