[navstik] Added a new board

Navstik STM32F4 autopilot.
This has the basic support for all the sensors and outputs most autopilots have. Still having issues with the i2c at boot, but seems to be a problem with STM32F4 autopilots.

https://wiki.paparazziuav.org/wiki/NavStik
http://www.navstik.org
Because of the IMU poweron in defined in the board. That was missing from my previous pull request.