Wrong Voltage Divider for FMUv5

[bkueng]

On FMUv5 the default voltage divider is 10.133333333f (via BOARD_BATTERY1_V_DIV), which is correct when using it with a Pixracer Power Board, but it's incorrect when using the provided Power Module. In that case it needs to be around 18.2.

I did not check the current, but it's likely wrong too.

[LorenzMeier]

After investigating the maximum voltage we can support with this divider I believe the current spec on FMUv5 is too limited and we need to go to a higher default divider to support 12S setups.

@bkueng Could you please change the divider to the correct value for the supplied power module and make sure we update our documentation accordingly?

Thanks!