utils/conv_gen.py: improve application flexibility

This change makes the conv_gen application more interactive
and flexible, allowing to generate not only code definitions
but also the test vectors and header files in the future.
Moreover, it becomes possible to select exact code family,
such as GSM, GMR etc.

Change-Id: I0b476b00234c17f78b41d695cf3bfd13edb64c28
2 files changed