Move RRC radio parameters file to DU

A number of radio-related RRC parameters, e.g., CellGroupConfig, "originate" at the DU and are sent to the CU for forwarding to the UE only. Similarly, there are additional parameters, e.g., RLC-BearerConfig (part of CellGroupConfig), that originate at the DU.

Hence, the DU decides about these parameters, depending on the MAC state and capabilities. To clarify this, move the existing

openair2/RRC/NR/nr_rrc_config.{c,h} => openair2/LAYER2/NR_MAC_gNB/nr_radio_config.{c,h}

So that developers know that while those are RRC parameters, they originate at the DU.

In other words, the CU/RRC is not supposed to use any of these functions in the RRC. Correspondingly, includes of this file have been cleaned up (and when they are not necessary at the MAC as well)