Ongoing work for adding per-thread UTCB structures.

Added setting of utcb address to l4_thread_control.
This is going to be moved to exchange_registers() since we need to pass
both the utcb physical and virtual address and exregs fits such context
modification better than thread_control.

tasks/libl4/include/l4lib/thread.h

@@ -0,0 +1,14 @@
+#ifndef __L4_THREAD_H__
+#define __L4_THREAD_H__
+
+#include <libl4/arch/utcb.h>
+#include <libl4/arch/types.h>
+
+struct l4_thread_struct {
+	l4id_t tlid;			/* Thread local id */
+	struct task_ids ids;		/* Thread L4-defined ids */
+	struct utcb *utcb;		/* Thread utcb */
+	unsigned long stack_start;	/* Thread start of stack */
+};
+
+#endif /* __L4_THREAD_H__ */