Kernel: Implemented priority inheritance for mutexes.

src/core/hle/kernel/thread.h

@@ -89,6 +89,12 @@ public:
      */
     void SetPriority(s32 priority);
 
+    /**
+     * Temporarily boosts the thread's priority until the next time it is scheduled
+     * @param priority The new priority
+     */
+    void BoostPriority(s32 priority);
+
     /**
      * Gets the thread's thread ID
      * @return The thread's ID