gallium/vl: Add plane order for Y8_400 format

Also add assert for unhandled format and remove assert for number of
components.

Cc: mesa-stable
Reviewed-by: Ruijing Dong <ruijing.dong@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32605>

src/gallium/auxiliary/vl/vl_video_buffer.c

@@ -93,9 +93,11 @@ vl_video_buffer_plane_order(enum pipe_format format)
    case PIPE_FORMAT_P010:
    case PIPE_FORMAT_P012:
    case PIPE_FORMAT_P016:
+   case PIPE_FORMAT_Y8_400_UNORM:
       return const_resource_plane_order_YUV;
 
    default:
+      assert(0);
       return NULL;
    }
 }
@@ -324,7 +326,6 @@ vl_video_buffer_sampler_view_components(struct pipe_video_buffer *buffer)
             goto error;
       }
    }
-   assert(component == VL_NUM_COMPONENTS);
 
    return buf->sampler_view_components;