Added I2C driver active check to driver initializations
Moved MPL3115A2 EXT init to device driver
Added EXT init and data ready read thread to MPU9150 driver
Flight-imu ext_pins functionality now contained in device drivers
Made MPU9150_{set,get} consistant with other drivers
Pruned unused data structures from MPU9150.h:
Reduced BQ3060 I2C timeout to be in line with other drivers