Address space creation/deletion implemented

- Proper releasing of user pmd and pgds when a space is not used.
- Proper releasing of task, space ids.

- At occasions a starting thread gets bogus SPSR, this needs investigating.
- At a very rare occasion arch_setup_new_thread() had a kernel data abort during
  register copying from one task to another. Needs investigating.

src/api/syscall.c

@@ -167,7 +167,7 @@ int sys_getid(syscall_context_t *regs)
 	struct ktcb *this = current;
 
 	ids->tid = this->tid;
-	ids->spid = this->spid;
+	ids->spid = this->space->spid;
 	ids->tgid = this->tgid;
 
 	return 0;