This uses the (modified) Osmocom asn1c on the (modified) SABP ASN.1
syntax to generate C code + header files for SABP parsing/encoding.
It also adds some helper code for message encoding and decoding as well
as a new libosmo-sabp shared library which can be used by programs to
implement SABP related functionality.
Change-Id: Ib9580d1af96354398da4c9f97b28a0e23d56e275