backends/drm: add some warnings for failing atomic tests

src/backends/drm/drm_gpu.cpp

@@ -328,6 +328,7 @@ bool DrmGpu::updateOutputs()
             }
         }
     } else {
+        qCWarning(KWIN_DRM, "Failed to find a working setup for new outputs!");
         for (const auto &pipeline : qAsConst(m_pipelines)) {
             pipeline->revertPendingChanges();
         }

src/backends/drm/drm_output.cpp

@@ -343,6 +343,7 @@ bool DrmOutput::setGammaRamp(const GammaRamp &gamma)
         m_renderLoop->scheduleRepaint();
         return true;
     } else {
+        qCWarning(KWIN_DRM) << "Applying gamma ramp failed on output" << this;
         m_pipeline->revertPendingChanges();
         return false;
     }