vm: replace vm-region with address-space

address-space is a non-recursive data structure, which contains a flat list of vm_areas representing
mapped vm-objects.

userspace programs can no longer create sub-address-spaces. instead, they can reserve portions of
the address space, and use that reserved space to create mappings.

init/main.c

@@ -112,7 +112,10 @@ void kernel_init(uintptr_t arg)
 	struct task *bootstrap_task = task_create("bootstrap", 9);
 	tracek("created bootstrap task (pid=%u)", bootstrap_task->t_id);
 
-	bsp_launch_async(&bsp, bootstrap_task);
+	status = bsp_launch_async(&bsp, bootstrap_task);
+	if (status != KERN_OK) {
+		printk("bsp launch failed with status %d", status);
+	}
 
 	hang();
 }