qapi/meson: Restrict qdev code to system-mode emulation

Beside a CPU device, user-mode emulation doesn't access
anything else from qdev subsystem.

Tools don't need anything from qdev.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210122204441.2145197-10-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/qapi/meson.build b/qapi/meson.build
index ab68e79..2839871 100644
--- a/qapi/meson.build
+++ b/qapi/meson.build
@@ -35,7 +35,6 @@
   'misc-target',
   'net',
   'pragma',
-  'qdev',
   'pci',
   'qom',
   'rdma',
@@ -49,6 +48,11 @@
   'ui',
   'yank',
 ]
+if have_system
+  qapi_all_modules += [
+    'qdev',
+  ]
+endif
 
 qapi_storage_daemon_modules = [
   'block-core',