bktr: Implement IVFC offset shifting

Fixes base game read errors

src/core/loader/loader.h

@@ -214,6 +214,15 @@ public:
         return true;
     }
 
+    /**
+     * Gets the difference between the start of the IVFC header and the start of level 6 (RomFS)
+     * data. Needed for bktr patching.
+     * @return IVFC offset for romfs.
+     */
+    virtual u64 ReadRomFSIVFCOffset() const {
+        return 0;
+    }
+
     /**
      * Get the title of the application
      * @param title Reference to store the application title into