posix: enable ROMFSROOT

This will copy the ROMFS into the build directory under etc/, and thus
needs a change of the PX4 startup parameters and mixer paths.

posix-configs/rpi/px4_fw.config

@@ -50,7 +50,7 @@ then
 fi
 
 navio_sysfs_rc_in start
-linux_pwm_out start -m ROMFS/px4fmu_common/mixers/AETRFG.main.mix
+linux_pwm_out start -m etc/mixers/AETRFG.main.mix
 
 logger start -t -b 200
 

posix-configs/rpi/px4_hil.config

@@ -36,7 +36,7 @@ mc_rate_control start
 mavlink start -x -u 14577 -r 1000000
 navio_sysfs_rc_in start
 pwm_out_sim start
-mixer load /dev/pwm_output0 ROMFS/px4fmu_common/mixers/quad_x.main.mix
+mixer load /dev/pwm_output0 etc/mixers/quad_x.main.mix
 
 logger start -t -b 200