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.

src/api/SConscript

@@ -3,7 +3,7 @@ Import('env')
 Import('config_symbols')
 
 # The set of source files associated with this SConscript file.
-src_local = ['kip.c', 'syscall.c', 'thread.c', 'ipc.c', 'space.c']
+src_local = ['kip.c', 'syscall.c', 'thread.c', 'ipc.c', 'space.c', 'mutex.c']
 
 obj = env.Object(src_local)