mixer: minor refactoring to reduce header include dependencies

- avoid including <px4_defines.h> from the math headers
- avoid driver include <drivers/drv_mixer.h> from the mixer

src/drivers/drv_mixer.h

@@ -71,31 +71,6 @@
 /** reset (clear) the mixer configuration */
 #define MIXERIOCRESET		_MIXERIOC(1)
 
-/** simple channel scaler */
-struct mixer_scaler_s {
-	float			negative_scale;
-	float			positive_scale;
-	float			offset;
-	float			min_output;
-	float			max_output;
-};
-
-/** mixer input */
-struct mixer_control_s {
-	uint8_t			control_group;	/**< group from which the input reads */
-	uint8_t			control_index;	/**< index within the control group */
-	struct mixer_scaler_s 	scaler;		/**< scaling applied to the input before use */
-};
-
-/** simple mixer */
-struct mixer_simple_s {
-	uint8_t			control_count;	/**< number of inputs */
-	struct mixer_scaler_s	output_scaler;	/**< scaling for the output */
-	struct mixer_control_s	controls[0];	/**< actual size of the array is set by control_count */
-};
-
-#define MIXER_SIMPLE_SIZE(_icount)	(sizeof(struct mixer_simple_s) + (_icount) * sizeof(struct mixer_control_s))
-
 /**
  * add a simple mixer in (struct mixer_simple_s *)arg
  */

src/drivers/uavcan/uavcan_main.cpp

@@ -59,6 +59,7 @@
 #include <uORB/topics/parameter_update.h>
 
 #include <drivers/drv_hrt.h>
+#include <drivers/drv_mixer.h>
 #include <drivers/drv_pwm_output.h>
 
 #include "uavcan_module.hpp"