AP_HAL_PX4: added mask to set_output_mode()

this allows for some groups using dshot and some not

libraries/AP_HAL_PX4/RCOutput.cpp

@@ -598,7 +598,7 @@ bool PX4RCOutput::enable_px4io_sbus_out(uint16_t rate_hz)
 /*
   setup output mode
  */
-void PX4RCOutput::set_output_mode(enum output_mode mode)
+void PX4RCOutput::set_output_mode(uint16_t mask, enum output_mode mode)
 {
     if (_output_mode == mode) {
         // no change

libraries/AP_HAL_PX4/RCOutput.h

@@ -35,7 +35,7 @@ public:
     void cork();
     void push();
 
-    void set_output_mode(enum output_mode mode) override;
+    void set_output_mode(uint16_t mask, enum output_mode mode) override;
 
     void timer_tick(void) override;
     bool enable_px4io_sbus_out(uint16_t rate_hz) override;