Do not re-read output configuration if the outputs didn't change

They would override KScreen in case we were using a dock station that
brings 2 displays.
We'd get:
- udev: event for the first hotplughed screen
- kwin: process all screens properly (both)
- kscreen: would offer the right configuration for such displays
- udev: process the event for the second hotplug udev event
- kwin: restore the configuration
- kscreen: would think this is a conscious decision and embrace it as a
configuration

With this change we are only re-reading the configuration in case the
outputs changed.

plugins/platforms/drm/drm_backend.cpp

@@ -341,11 +341,14 @@ bool DrmBackend::updateOutputs()
     if (m_gpus.size() == 0) {
         return false;
     }
+    const auto oldOutputs = m_outputs;
     for (auto gpu : m_gpus)
         gpu->updateOutputs();
     
     std::sort(m_outputs.begin(), m_outputs.end(), [] (DrmOutput *a, DrmOutput *b) { return a->m_conn->id() < b->m_conn->id(); });
-    readOutputsConfiguration();
+    if (oldOutputs != m_outputs) {
+        readOutputsConfiguration();
+    }
     updateOutputsEnabled();
     if (!m_outputs.isEmpty()) {
         emit screensQueried();

plugins/platforms/drm/drm_output.cpp

@@ -352,7 +352,7 @@ void DrmOutput::initEdid(drmModeConnector *connector)
         }
     }
     if (!edid) {
-        qDebug() << "could not find edid for connector" << connector << connector->connector_id;
+        qCWarning(KWIN_DRM) << "Could not find edid for connector" << connector << connector->connector_id;
         return;
     }