Assign threads to PD at its creation time

This patch replaces the former 'Pd_session::bind_thread' function by a
PD-capability argument of the 'Cpu_session::create_thread' function, and
removes the ancient thread-start protocol via 'Rm_session::add_client' and
'Cpu_session::set_pager'. Threads are now bound to PDs at their creation
time and implicitly paged according to the address space of the PD.

Note the API change:

This patch changes the signature of the 'Child' and 'Process' constructors.
There is a new 'address_space' argument, which represents the region map
representing the child's address space. It is supplied separately to the
PD session capability (which principally can be invoked to obtain the
PD's address space) to allow the population of the address space
without relying on an 'Pd_session::address_space' RPC call.
Furthermore, a new (optional) env_pd argument allows the explicit
overriding of the PD capability handed out to the child as part of its
environment. It can be used to intercept the interaction of the child
with its PD session at core. This is used by Noux.

Issue #1938

repos/base-nova/include/nova/native_thread.h

@@ -35,6 +35,8 @@ struct Genode::Native_thread
 	/* receive window for capability selectors received at the server side */
 	Receive_window rcv_window;
 
+	Native_capability pager_cap;
+
 	Native_thread() : ec_sel(INVALID_INDEX),
 	                  exc_pt_sel(INVALID_INDEX), is_vcpu(false) { }
 };