Use WANT_ADXL345 and WANT_MPU9250 instead of WANT_SENSOR_ADXL345 and
WANT_SENSOR_MPU9250. This makes these definitions similar to the
other accelerometer defintions.
Order menu so accelerometers are close to each other in the menu.
Simplify Makefile as Kconfig already assures a symbol will only be
defined if its dependencies are met.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>