[peripherals] add mpu9250 driver
[uart] Fix weak handler
[mpu9250] add test module and imu subsystem
[sensors] Added the AKM 8963 Magnetometer
[peripheral] fix some stuff in the ak8963 driver
[peripheral] update mpu9250 driver, imu and module as well
Merge pull request #953 from paparazzi/mpu9250

Driver for the MPU9250