Make AX.25, DMR, P25, NXDN and FM selectable at compile time.

FMDirectForm1.h

@@ -29,6 +29,10 @@ THE SOFTWARE.
 
 // based on https://raw.githubusercontent.com/berndporr/iir_fixed_point/master/DirectFormI.h
 
+#include "Config.h"
+
+#if defined(MODE_FM)
+
 #include <cstdint>
 
 #ifndef DIRECTFORMI_H_
@@ -108,4 +112,7 @@ private:
 	q31_t c_a1,c_a2; // IIR
 };
 
-#endif /* DIRECTFORMI_H */
+#endif /* DIRECTFORMI_H */
+
+#endif
+