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
diff --git a/src/gsm/Makefile.am b/src/gsm/Makefile.am
index 4ec441f..653bdb9 100644
--- a/src/gsm/Makefile.am
+++ b/src/gsm/Makefile.am
@@ -35,6 +35,6 @@
 
 # Convolutional codes generation
 gsm0503_conv.c:
-	$(AM_V_GEN)python2 $(top_srcdir)/utils/conv_gen.py
+	$(AM_V_GEN)python2 $(top_srcdir)/utils/conv_gen.py gen_codes gsm
 
 CLEANFILES = gsm0503_conv.c