Automatic generation of a header file using a C program built during
build of osmo-bts creates several problems when cross-compiling.
The generated header file is only 59 lines long, so let's have it
generated in order to avoid having to call the helper program every
time.
A Makefile target is added to easily regenerate the file manually in
case it's needed:
make -C contrib/ber/ update_codec_bit_class_h
Fixes: acf0f0f0bb
Change-Id: I97efdb4ee00537fcae191b4267d0211d582ef372
