Extend base-hw specific vm-session (fix #738)

Introduce pause syscall for VM objects, and extend the vm-session interface
to support it.

base-hw/include/vm_session/client.h

@@ -41,8 +41,8 @@ namespace Genode
 		void exception_handler(Signal_context_capability handler) {
 			call<Rpc_exception_handler>(handler); }
 
-		void run() {
-			call<Rpc_run>(); }
+		void run()   { call<Rpc_run>();   }
+		void pause() { call<Rpc_pause>(); }
 	};
 }