drm/amdgpu/display: fix dal_allocation documentation

Add missing structure elements.

Fixes: 0dd79532 ("drm/amdgpu/display: Implement functions to let DC allocate GPU memory")
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -139,6 +139,10 @@ struct amdgpu_dm_backlight_caps {
 
 /**
  * struct dal_allocation - Tracks mapped FB memory for SMU communication
+ * @list: list of dal allocations
+ * @bo: GPU buffer object
+ * @cpu_ptr: CPU virtual address of the GPU buffer object
+ * @gpu_addr: GPU virtual address of the GPU buffer object
  */
 struct dal_allocation {
 	struct list_head list;