Remove mpu6050_scale from core_t by providing a sensor independent way

of determining a revision code.  Previously there was mpu6050 specific
code in cli.c (the status command).

Finally this commit has removed all non-serial port configuration
settings from core_t so that a future commit can refactor core_t to
reduce dependencies on serial port code.

In doing this I also noted from other source code that the MPU6050
accelerometer trim for some revisions appeared to be incorrectly set to
255 * 8 instead of 256 * 8.

src/sensors_common.h

@@ -31,6 +31,7 @@ typedef struct sensor_t
     sensorReadFuncPtr read;                                 // read 3 axis data function
     sensorReadFuncPtr temperature;                          // read temperature if available
     float scale;                                            // scalefactor (currently used for gyro only, todo for accel)
+    char revisionCode;                                      // a revision code for the sensor, if known
 } sensor_t;
 
 extern int16_t heading;