crazyflie: fix PWM channel ordering

Channels belonging to a certain timer were not all grouped together.
This is required by the .first_channel_index and .last_channel_index data
members.

We introduce a new mixer geometry to solve the problem.

ROMFS/px4fmu_common/init.d/airframes/4900_crazyflie

@@ -17,7 +17,7 @@
 #
 sh /etc/init.d/rc.mc_defaults
 
-set MIXER quad_x
+set MIXER quad_x_cw
 set PWM_OUT 1234
 if [ $AUTOCNF = yes ]
 then

ROMFS/px4fmu_common/mixers/CMakeLists.txt

@@ -71,6 +71,7 @@ px4_add_romfs_files(
 	quad_+_vtol.main.mix
 	quad_w.main.mix
 	quad_x.main.mix
+	quad_x_cw.main.mix
 	quad_x_vtol.main.mix
 	stampede.main.mix
 	tri_y_yaw-.main.mix

ROMFS/px4fmu_common/mixers/quad_x_cw.main.mix

@@ -0,0 +1,5 @@
+# @board px4_fmu-v2 exclude
+# Quad X with clock-wise motor assigment
+
+R: 4xcw 10000 10000 10000 0
+