hdd: make speed preset configurable

This includes settings UI for Qt

src/qt/qt_harddiskdialog.hpp

@@ -21,6 +21,7 @@ public:
     uint32_t cylinders() const { return cylinders_; }
     uint32_t heads() const { return heads_; }
     uint32_t sectors() const { return sectors_; }
+    uint32_t speed() const;
 
 signals:
     void fileProgress(int i);