gpu/kms: Turn off CRTCs as well for DPMS

This avoids some issues which could happen on some setups[0] due to
meta-native-renderer.c:dummy_power_save_page_flip →
meta_onscreen_native_swap_drm_fb implicitly turning of the primary
plane (by destroying the KMS framebuffer assigned to it):

* drmModeObjectSetProperty could return an "Invalid argument" error
  between setting a non-empty cursor with drmModeSetCursor(2) and
  enabling the primary plane again:

  Failed to DPMS: Failed to set connector 69 property 2: Invalid argument

  (This was harmless other than the error message, as we always re-set
  a mode on the CRTC after setting the DPMS property to on, which
  enables the primary plane and implicitly sets the DRM property to on)

* drmModeSetCursor(2) could return an "Invalid argument" error between
  setting the DPMS property to on and enabling the primary plane again:

  Failed to set hardware cursor (drmModeSetCursor failed: Invalid argument), using OpenGL from now on

[0] E.g. with the amdgpu DC display code.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1240


(cherry picked from commit 2e5b767c01)

src/backends/native/meta-gpu-kms.c

@@ -232,14 +232,28 @@ meta_gpu_kms_set_power_save_mode (MetaGpuKms    *gpu_kms,
                                   uint64_t       state,
                                   MetaKmsUpdate *kms_update)
 {
+  MetaGpu *gpu = META_GPU (gpu_kms);
   GList *l;
 
-  for (l = meta_gpu_get_outputs (META_GPU (gpu_kms)); l; l = l->next)
+  for (l = meta_gpu_get_outputs (gpu); l; l = l->next)
     {
       MetaOutput *output = l->data;
 
       meta_output_kms_set_power_save_mode (output, state, kms_update);
     }
+
+  if (state != META_POWER_SAVE_ON)
+    {
+      /* Turn off CRTCs for DPMS */
+      for (l = meta_gpu_get_crtcs (gpu); l; l = l->next)
+        {
+          MetaCrtcKms *crtc_kms = META_CRTC_KMS (l->data);
+
+          meta_kms_update_mode_set (kms_update,
+                                    meta_crtc_kms_get_kms_crtc (crtc_kms),
+                                    NULL, NULL);
+        }
+    }
 }
 
 gboolean