libcamera: controls: Make ControList constructor public

We need to construct empty ControlList objects to serialization. Make
the constructor public.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

include/libcamera/controls.h

@@ -189,6 +189,7 @@ private:
 	using ControlListMap = std::unordered_map<unsigned int, ControlValue>;
 
 public:
+	ControlList();
 	ControlList(const ControlIdMap &idmap, ControlValidator *validator = nullptr);
 	ControlList(const ControlInfoMap &info, ControlValidator *validator = nullptr);