move implementation to cc file to avoid
[build] /bin/ld: CMakeFiles/rrc_nr_asn1_test.dir/rrc_nr_test.cc.o: in function `asn1::rrc_nr::setup_release_c<asn1::rrc_nr::pdcch_serving_cell_cfg_s>::set_setup()':
[build] /home/anpu/src/srsLTE/lib/include/srsran/asn1/rrc_nr.h:2276: undefined reference to `asn1::rrc_nr::setup_release_c<asn1::rrc_nr::pdcch_serving_cell_cfg_s>::set(asn1::rrc_nr::setup_release_c<asn1::rrc_nr::pdcch_serving_cell_cfg_s>::types_opts::options)'
[build] clang: error: linker command failed with exit code 1 (use -v to see invocation)
- use const char* instead of std::string in enumerated<>::to_string() to avoid mallocs.
- Remove the use of "typedef", and use "using" keyword instead.
- Fix rrc_nr::setup_release_c<>::to_string() broken linkage.