Schedule policy for stm32f4discovery(stm32f407)

I'm using Nuttx V10.2.
I believe nutxx's standard scheduling policy is FIFO.
However, with STM32F407, if two tasks with the same priority are started, the RR scheduling policy will be applied.

This is that logging.
Two tasks with the same priority started running on 4808Tick.
```
task_create name:myTask1 priority:100
task_create name:myTask2 priority:100
myTask1 start PID:12 loop:50000000 wait:0 system_timer:4808
myTask2 start PID:13 loop:50000000 wait:0 system_timer:4808
nsh> ps
PID PRI POLICY TYPE NPX STATE EVENT SIGMASK STACK COMMAND
0 0 FIFO Kthread N-- Ready 00000000 001000 Idle Task
2 100 RR Task --- Running 00000000 002032 init
12 100 RR Task --- Ready 00000000 002008 myTask1 50000000 0
13 100 RR Task --- Ready 00000000 002008 myTask2 50000000 0
nsh> myTask1 end PID:12 system_timer:5336
myTask2 end PID:13 system_timer:5344
```