clarify typed/untyped resources and improve support for untyped resources
A typed resource is a virgl_resource with a pipe_resource, because pipe_resource provides both the storage and the type information (format, width, height, etc.). An untyped resource is a virgl_resource without a pipe_resource. This will be the only kind of resources created from a VkDeviceMemory.
This MR fixes virgl_renderer_resource_get_map_info and virgl_renderer_export_query for untyped resources.