Thread API cleanup

This patch cleans up the thread API and comes with the following
noteworthy changes:

- Introduced Cpu_session::Weight type that replaces a formerly used
  plain integer value to prevent the accidental mix-up of
  arguments.
- The enum definition of Cpu_session::DEFAULT_WEIGHT moved to
  Cpu_session::Weight::DEFAULT_WEIGHT
- New Thread constructor that takes a 'Env &' as first argument.
  The original constructors are now marked as deprecated. For the
  common use case where the default 'Weight' and 'Affinity' are
  used, a shortcut is provided. In the long term, those two
  constructors should be the only ones to remain.
- The former 'Thread<>' class template has been renamed to
  'Thread_deprecated'.
- The former 'Thread_base' class is now called 'Thread'.
- The new 'name()' accessor returns the thread's name as 'Name'
  object as centrally defined via 'Cpu_session::Name'. It is meant to
  replace the old-fashioned 'name' method that takes a buffer and size
  as arguments.
- Adaptation of the thread test to the new API

Issue #1954

repos/os/src/server/tz_vmm/block.cc

@@ -269,7 +269,7 @@ class Device_registry
 /**
  * Thread that listens to device interrupts and propagates them to a VM
  */
-class Callback : public Thread<8192>
+class Callback : public Thread_deprecated<8192>
 {
 	private:
 
@@ -324,11 +324,11 @@ class Callback : public Thread<8192>
 		 */
 		Callback(Vm_base * const vm)
 		:
-			Thread<8192>("blk-signal-thread"),
+			Thread_deprecated<8192>("blk-signal-thread"),
 			_ready_lock(Lock::LOCKED),
 			_vm(vm)
 		{
-			Thread_base::start();
+			Thread::start();
 			_ready_lock.lock();
 		}
 };

repos/os/src/server/tz_vmm/spec/imx53/main.cc

@@ -45,7 +45,7 @@ namespace Vmm {
 }
 
 
-class Vmm::Vmm : public Thread<8192>
+class Vmm::Vmm : public Thread_deprecated<8192>
 {
 	private:
 
@@ -128,7 +128,7 @@ class Vmm::Vmm : public Thread<8192>
 	public:
 
 		Vmm(Vm *vm)
-		: Thread<8192>("vmm"),
+		: Thread_deprecated<8192>("vmm"),
 		  _vm(vm),
 		  _m4if_io_mem(Board_base::M4IF_BASE, Board_base::M4IF_SIZE),
 		  _m4if((addr_t)env()->rm_session()->attach(_m4if_io_mem.dataspace()))