Refactor radio-related RRC parameters and further cleanup

• Move radio-related/DU RRC parameters to a single file nr_rrc_config.c:
  • MIB generation
  • SIB1 generation
  • initial (SA) CellGroupConfig
  • default (NSA) CellGroupConfig
    • the latter two still have some RB parameters that might go out
  • Reuse existing bearer configuration functions to replace duplicated code for do-ra/phytest configuration code in RLC (nr_rlc_oai_api.c) and PDCP (nr_pdcp_oai_api.c) layers
  • I need to rewrite the commit message of 3f09b9fb
  • We can rename the nr_rrc_config.c file, please advise
• Lots of cleanup
  • Remove commented code
  • New functions to "encapsulate" RRC access to MAC
  • Remove unused function parameters
  • Remove write-only or unused variables
  • Make many functions in (gNB) MAC main.c and nr_rrc_config.c static