Extend Cpu_session with thread-affinity API

This patch introduces the functions 'affinity' and 'num_cpus' to the CPU
session interface. The interface extension will allow the assignment of
individual threads to CPUs. At this point, it is just a stub with no
actual platform support.

base-host/src/core/include/platform_thread.h

@@ -92,9 +92,9 @@ namespace Genode {
 			unsigned long pager_object_badge() const;
 
 			/**
-			 * Set the executing CPU for this thread.
+			 * Set the executing CPU for this thread
 			 */
-			void set_cpu(unsigned int cpu_no);
+			void affinity(unsigned cpu);
 
 			/**
 			 * Get thread name

base-host/src/core/platform_thread.cc

@@ -20,7 +20,7 @@
 using namespace Genode;
 
 
-void Platform_thread::set_cpu(unsigned int cpu_no)
+void Platform_thread::affinity(unsigned int cpu_no)
 {
 	PERR("not yet implemented");
 }