GPS is working on one of my two Erle Rover on APM Planner.
For everyone, the solution was to adding sleep(10) at the begining of APM.sh and configure GPS on ttyS0 (-B /dev/ttyS0) and to finish writing enable_uart=1 at the end of /boot/config.txt which permit to activate ttyS0.
Moreover, without the sleep(10) I wasn't able to change the flight mode of the rover by APM Planner.
I did the same on my second Erle brain but it still doesn't working. I will try to reconfigure this one.
I hope it will be usefull for some Erle users.