PX4 System change to allow way to override the PWM_.*_{MIN|MAX} values

Add PX4_PWM_ALTERNATE_RANGES in suport of a board agnostic way
 to override the PWM_.*_{MIN|MAX} values

src/drivers/drv_pwm_output.h

@@ -75,18 +75,11 @@ __BEGIN_DECLS
  */
 //#define PWM_OUTPUT_MAX_CHANNELS	16
 
-#if defined(CONFIG_ARCH_BOARD_CRAZYFLIE)
-
-/* PWM directly wired to transistor. Duty cycle directly corresponds to power */
-#define PWM_LOWEST_MIN 0
-#define PWM_MOTOR_OFF	0
-#define PWM_DEFAULT_MIN 0
-#define PWM_HIGHEST_MIN 0
-#define PWM_HIGHEST_MAX 255
-#define PWM_DEFAULT_MAX 255
-#define PWM_LOWEST_MAX 255
-
-#else
+/* Use defaults unless the board override the defaults by providing
+ * PX4_PWM_ALTERNATE_RANGES and a replacement set of
+ * constants
+ */
+#if !defined(PX4_PWM_ALTERNATE_RANGES)
 
 /**
  * Lowest minimum PWM in us
@@ -123,7 +116,7 @@ __BEGIN_DECLS
  */
 #define PWM_LOWEST_MAX 200
 
-#endif
+#endif // PX4_PWM_ALTERNATE_RANGES
 
 /**
  * Do not output a channel with this value