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>

src/libcamera/controls.cpp

@@ -590,6 +590,17 @@ void ControlInfoMap::generateIdmap()
  * controls.
  */
 
+/**
+ * \brief Construct a ControlList not associated with any object
+ *
+ * This constructor is meant to support ControlList serialization and shall not
+ * be used directly by application.
+ */
+ControlList::ControlList()
+	: validator_(nullptr), idmap_(nullptr)
+{
+}
+
 /**
  * \brief Construct a ControlList with an optional control validator
  * \param[in] idmap The ControlId map for the control list target object