iris: Make various classes inherit from u_threaded_context base classes

iris: Make various classes inherit from u_threaded_context base classes

u_threaded_context requires various objects to inherit from a new
threaded_foo base class rather than directly from pipe_foo.  This
patch does most of the mechanical changes required for that.

It also initializes the new threaded_resource fields.

Reviewed-by: Zoltán Böszörményi <zboszor@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8964>