BlockParam: remove _extern_address and create a new class BlockParamExt for this

In most cases, _extern_address was unused, thus wasting cycles & RAM. This
adds a separate class BlockParamExt with the field and uses it in ekf2_main

Frees roughly 0.5KB of RAM on Pixracer

src/lib/controllib/block/BlockParam.hpp

@@ -77,21 +77,45 @@ class BlockParam : public BlockParamBase
 {
 public:
 	BlockParam(Block *block, const char *name,
-		   bool parent_prefix = true, T *extern_address = NULL);
+		   bool parent_prefix = true);
 	BlockParam(const BlockParam &) = delete;
 	BlockParam &operator=(const BlockParam &) = delete;
 
 	T get();
 	void commit();
 	void set(T val);
-	void update();
+	void update() override;
 	virtual ~BlockParam();
 protected:
 	T _val;
-	T *_extern_address;
 };
 
 typedef BlockParam<float> BlockParamFloat;
 typedef BlockParam<int> BlockParamInt;
 
+
+/**
+ * Same as BlockParam, but in addition with a pointer to an external field that will be
+ * set to the value of the parameter.
+ * (BlockParam should be prefered over this)
+ */
+template <class T>
+class BlockParamExt : public BlockParam<T>
+{
+public:
+	BlockParamExt(Block *block, const char *name,
+		      bool parent_prefix, T &extern_val);
+	BlockParamExt(const BlockParamExt &) = delete;
+	BlockParamExt &operator=(const BlockParamExt &) = delete;
+
+	void set(T val);
+	void update() override;
+	virtual ~BlockParamExt();
+protected:
+	T &_extern_val;
+};
+
+typedef BlockParamExt<float> BlockParamExtFloat;
+typedef BlockParamExt<int> BlockParamExtInt;
+
 } // namespace control