Streamline exception types

This patch reduces the number of exception types by facilitating
globally defined exceptions for common usage patterns shared by most
services. In particular, RPC functions that demand a session-resource
upgrade not longer reflect this condition via a session-specific
exception but via the 'Out_of_ram' or 'Out_of_caps' types.

Furthermore, the 'Parent::Service_denied', 'Parent::Unavailable',
'Root::Invalid_args', 'Root::Unavailable', 'Service::Invalid_args',
'Service::Unavailable', and 'Local_service::Factory::Denied' types have
been replaced by the single 'Service_denied' exception type defined in
'session/session.h'.

This consolidation eases the error handling (there are fewer exceptions
to handle), alleviates the need to convert exceptions along the
session-creation call chain, and avoids possible aliasing problems
(catching the wrong type with the same name but living in a different
scope).

repos/ports/include/vmm/guest_memory.h

@@ -66,7 +66,7 @@ struct Vmm::Virtual_reservation : private Rm_connection, Region_map_client
 			env.rm().attach_at(Region_map_client::dataspace(), PAGE_SIZE, 0,
 			                   PAGE_SIZE);
 
-		} catch (Rm_session::Region_conflict) {
+		} catch (Region_map::Region_conflict) {
 			error("region conflict while attaching guest-physical memory");
 		}
 	}

repos/ports/include/vmm/vcpu_dispatcher.h

@@ -116,7 +116,7 @@ class Vmm::Vcpu_dispatcher : public T
 				Capability_space::import(T::native_thread().ec_sel);
 
 			Untyped_capability handler =
-				retry<Genode::Pd_session::Out_of_metadata>(
+				retry<Genode::Out_of_ram>(
 					[&] () {
 						/* manually define selector used for RPC result */
 						Thread::myself()->native_thread().client_rcv_sel = exc_base + EV;