TRIG_PINS: allow triggering on 78 while still using the lower 6 pins for pwm

ROMFS/px4fmu_common/init.d/rcS

@@ -406,15 +406,22 @@ else
 
 	if param greater TRIG_MODE 0
 	then
-		# We ONLY support trigger on pins 5 and 6 when simultanously using AUX for actuator output.
+		# We ONLY support trigger on pins 5+6 or 7+8 when simultanously using AUX for actuator output.
 		if param compare TRIG_PINS 56
 		then
 			# clear pins 5 and 6
 			set FMU_MODE pwm4
 			set AUX_MODE pwm4
 		else
-			set FMU_MODE none
+			if param compare TRIG_PINS 78
-			set AUX_MODE none
+			then
+				# clear pins 7 and 8
+				set FMU_MODE pwm6
+				set AUX_MODE pwm6
+			else
+				set FMU_MODE none
+				set AUX_MODE none
+			fi
 		fi
 
 		camera_trigger start