upower: add withSystemd option

Since 7f2a6f17fc ("xdg-desktop-portal-gtk: Enable all default
portals unconditionally"), building upower is necessary to build
xdg-desktop-portal-gtk, but it wasn't possible for systems that can't
use systemd.

I've called the option "withSystemd" as it's the most common name for
this kind of option in Nixpkgs, and it's consistent with the package's
"withIntrospection" argument (though not "useIMobileDevice").

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

@@ -17,7 +17,6 @@
 , libusb1
 , glib
 , gettext
-, systemd
 , nixosTests
 , useIMobileDevice ? true
 , libimobiledevice
@@ -26,6 +25,8 @@
 , withIntrospection ? lib.meta.availableOn stdenv.hostPlatform gobject-introspection && stdenv.hostPlatform.emulatorAvailable buildPackages
 , buildPackages
 , gobject-introspection
+, withSystemd ? lib.meta.availableOn stdenv.hostPlatform systemd
+, systemd
 }:
 
 assert withDocs -> withIntrospection;
@@ -82,7 +83,6 @@ stdenv.mkDerivation (finalAttrs: {
     libgudev
     libusb1
     udev
-    systemd
   ] ++ lib.optionals withIntrospection [
     # Duplicate from nativeCheckInputs until https://github.com/NixOS/nixpkgs/issues/161570 is solved
     umockdev
@@ -94,6 +94,8 @@ stdenv.mkDerivation (finalAttrs: {
       pp.pygobject3
       pp.packaging
     ]))
+  ] ++ lib.optionals withSystemd [
+    systemd
   ] ++ lib.optionals useIMobileDevice [
     libimobiledevice
   ];