Added mutex_control syscall for userspace mutexes.

- Compiles and Codezero runs as normal without touching mutex implementation
- Mutex implementation needs testing.

The mutex control syscall allows userspace programs to declare any virtual
address as a mutex lock and ask for help from the kernel syscall
for resolving locking contentions.

tasks/libl4/src/init.c

@@ -23,6 +23,7 @@ __l4_space_control_t __l4_space_control = 0;
 __l4_exchange_registers_t __l4_exchange_registers = 0;
 __l4_kmem_control_t __l4_kmem_control = 0;
 __l4_time_t __l4_time = 0;
+__l4_mutex_control_t __l4_mutex_control = 0;
 
 struct kip *kip;
 
@@ -54,5 +55,6 @@ void __l4_init(void)
 			(__l4_exchange_registers_t)kip->exchange_registers;
 	__l4_kmem_control =	(__l4_kmem_control_t)kip->kmem_control;
 	__l4_time =		(__l4_time_t)kip->time;
+	__l4_mutex_control=	(__l4_mutex_control_t)kip->mutex_control;
 }