drm/amdgpu/display: these forward declarations are not used

Remove them.
Signed-off-by: ZhiJie.Zhang <zhangzhijie@loongson.cn>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -58,10 +58,10 @@
 /* Forward declarations */
 struct amdgpu_device;
 struct drm_device;
-struct amdgpu_dm_irq_handler_data;
 struct dc;
 struct amdgpu_bo;
 struct dmub_srv;
+struct dc_plane_state;
 
 struct common_irq_params {
 	struct amdgpu_device *adev;
@@ -419,11 +419,6 @@ struct amdgpu_dm_connector {
 
 extern const struct amdgpu_ip_block_version dm_ip_block;
 
-struct amdgpu_framebuffer;
-struct amdgpu_display_manager;
-struct dc_validation_set;
-struct dc_plane_state;
-
 struct dm_plane_state {
 	struct drm_plane_state base;
 	struct dc_plane_state *dc_state;