udev: choose implementation with availableOn check

This means we don't have to repeat the list of platforms we can't use
systemd on, and can instead rely on the list in systemd's derivation.
This means that the right thing will happen on other platforms that
can't use systemd, one example being microblaze.

pkgs/top-level/all-packages.nix

···
   };
 
   udev =
-    if (with stdenv.hostPlatform; isLinux && isStatic) then libudev-zero
-    else systemdLibs;
+    if lib.meta.availableOn stdenv.hostPlatform systemdLibs then systemdLibs
+    else libudev-zero;
 
   sysvtools = sysvinit.override {
     withoutInitTools = true;