drm/amd/display: Fix warning

[Why]
- Wrong scope for ifdef
- Missing struct description

[How]
Move ifdef and add comment
Tested-by: NDaniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: NQingqing Zhuo <qingqing.zhuo@amd.com>
Reviewed-by: NNicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: NEryk Brol <eryk.brol@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -977,11 +977,12 @@ static void event_mall_stutter(struct work_struct *work)
 	else
 		dm->active_vblank_irq_count--;
 
-
+#if defined(CONFIG_DRM_AMD_DC_DCN3_0)
 	dc_allow_idle_optimizations(
 		dm->dc, dm->active_vblank_irq_count == 0);
 
 	DRM_DEBUG_DRIVER("Allow idle optimizations (MALL): %d\n", dm->active_vblank_irq_count == 0);
+#endif
 
 
 	mutex_unlock(&dm->dc_lock);

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h

@@ -245,12 +245,12 @@ struct amdgpu_display_manager {
 	 */
 	struct mutex audio_lock;
 
+#if defined(CONFIG_DRM_AMD_DC_DCN)
 	/**
-	 * @vblank_work_lock:
+	 * @vblank_lock:
 	 *
 	 * Guards access to deferred vblank work state.
 	 */
-#if defined(CONFIG_DRM_AMD_DC_DCN)
 	spinlock_t vblank_lock;
 #endif
 
@@ -342,6 +342,11 @@ struct amdgpu_display_manager {
 #endif
 
 #if defined(CONFIG_DRM_AMD_DC_DCN)
+	/**
+	 * @vblank_workqueue:
+	 *
+	 * amdgpu workqueue during vblank
+	 */
 	struct vblank_workqueue *vblank_workqueue;
 #endif
 
@@ -360,12 +365,15 @@ struct amdgpu_display_manager {
 	 */
 	const struct gpu_info_soc_bounding_box_v1_0 *soc_bounding_box;
 
+#if defined(CONFIG_DRM_AMD_DC_DCN)
 	/**
 	 * @active_vblank_irq_count:
 	 *
 	 * number of currently active vblank irqs
 	 */
 	uint32_t active_vblank_irq_count;
+#endif
+
 #if defined(CONFIG_DRM_AMD_SECURE_DISPLAY)
 	struct crc_rd_work *crc_rd_wrk;
 #endif