For now it is only checking if there is a external HMC5883, if
necessary more compass should be added and probe.

AeroFC is updated by Aero board using the UART between AeroFC
and Aero board.

This script will copy firmware and px_uploader.py to Aero board and run
px_uploader.py with the correct paremeters. User only needs to have a
network connection (Ethernet over USB or WiFi) with Aero board to update
AeroFC firmware. The IP/hostname can be given by AERO_HOSTNAME
environment variable.

Right now it's only possible to use ttyS2 as the UART for connecting a
companion computer. Add a variable that can be set so other boards may
be better supported.

Or mixer load will fail

We export an "empty" table, but there's no protection when doing
ioctl().

So it just does rcin and does not try to do the other initializations.

As ASC use a non-standard UART for mavlink it is necessary check for
the board name and set SYS_AUTOSTART to initialize mavlink on the
right interface otherwise there is no way to change the SYS_AUTOSTART.

Correct set pin mux and removed unused interfaces.

MPU6500, MS5611 and HMC5883 only power on when GPIO_SENSORS_POWER is
set.

Battery voltage and current will be read in another way in future.

Like in bootloader, use the centered LED to show activity.

SPI bus 1 is the bus connected to MPU6500, so remove SPI bus 3 and 4.
Also remove everything else related to SPI that this board doesn't have.

Remove what's not used like SPI and UART ports, ADC, etc. Add UART5 and
I2C1 that are going to be used.

This also received contribution from
José Roberto de Souza <jose.souza@intel.com>.

This allows to set the environment variable NO_PXH to start SITL without
the interactive pxh> shell. For this, px4 is called with the -d arg
which sets it to deamon mode.

This feature is handy to script sitl_run.sh.