AP_RPM: add static create method

libraries/AP_RPM/AP_RPM.h

@@ -26,10 +26,16 @@ class AP_RPM_Backend;
 
 class AP_RPM
 {
-public:
     friend class AP_RPM_Backend;
 
-    AP_RPM(void);
+public:
+    static AP_RPM create() { return AP_RPM{}; }
+
+    constexpr AP_RPM(AP_RPM &&other) = default;
+
+    /* Do not allow copies */
+    AP_RPM(const AP_RPM &other) = delete;
+    AP_RPM &operator=(const AP_RPM&) = delete;
 
     // RPM driver types
     enum RPM_Type {
@@ -89,6 +95,8 @@ public:
     bool enabled(uint8_t instance) const;
 
 private:
+    AP_RPM();
+
     RPM_State state[RPM_MAX_INSTANCES];
     AP_RPM_Backend *drivers[RPM_MAX_INSTANCES];
     uint8_t num_instances:2;