- Limit scope of get_default_rbconfig function: from asn1_msg.c/.h to rrc_gNB_nsa.c where it's used
- Create new rrc_gNB_asn1.c/h files for ASN.1 utility functions: they can be used in other RRC files
- Add nr_rrc_build_pdcp_config_ie function for building PDCP configuration IEs
- Update get_default_rbconfig to use the new PDCP config builder
- Add rrc_gNB_asn1.c to CMakeLists.txt build configuration