Thread: Implement priority boost for starved threads.

SVC: Return correct error code on invalid CreateThread processor ID.

SVC: Assert when creating a thread with an invalid userland priority.

src/common/thread_queue_list.h

@@ -40,6 +40,18 @@ struct ThreadQueueList {
         return -1;
     }
 
+    T get_first() {
+        Queue *cur = first;
+        while (cur != nullptr) {
+            if (!cur->data.empty()) {
+                return cur->data.front();
+            }
+            cur = cur->next_nonempty;
+        }
+
+        return T();
+    }
+
     T pop_first() {
         Queue *cur = first;
         while (cur != nullptr) {
@@ -79,6 +91,12 @@ struct ThreadQueueList {
         cur->data.push_back(thread_id);
     }
 
+    void move(const T& thread_id, Priority old_priority, Priority new_priority) {
+        remove(old_priority, thread_id);
+        prepare(new_priority);
+        push_back(new_priority, thread_id);
+    }
+
     void remove(Priority priority, const T& thread_id) {
         Queue *cur = &queues[priority];
         boost::remove_erase(cur->data, thread_id);