CMSIS-DSP: Improve doxygen.
* This is only valid for scalar. When vector architecture is
* supporting f16 then it can't be disabled.
*
+ * - ARM_MATH_AUTOVECTORIZE:
+ *
+ * With Helium or Neon, disable the use of vectorized code with C intrinsics
+ * and use pure C instead. The vectorization is then done by the compiler.
+ *
* <hr>
* \section pack CMSIS-DSP in ARM::CMSIS Pack
*
