[sensors] Minor tuning of hal definition

  * Swap GEOMAGNETIC_FIELD with MAGNETIC_FIELD for more accurate
    definition.
  * Clarify that string type will be omitted for well defined sensor
    types.
  * Remove legacy 8-bit restriction to sensor handle. This is an
    unnecessary limit for since long time ago. Still leave the define
    for code compatibility and change the value to 32.
  * update sensors-base.h with companion .hal file change.

Test: test with sensorlogger, all sensor works
Change-Id: I6ff7022146eb25f7efdce87b70bf5ed488a70c6d
2 files changed