Make separate header for nr_pdcp instead of using 4G pdcp

Creates function that have nr_pdcp_ prepended to their name, and change
the signature of some functions for the 5G PDCP:

- nr_pdcp_layer_init()
- nr_pdcp_data_req()
- nr_pdcp_remove_UE()
- nr_pdcp_config_set_security()
- nr_pdcp_remove_UE()
- Make separate functions for nr_pdcp_data_req_srb/drb()

openair2/F1AP/f1ap_cu_rrc_message_transfer.c

@@ -37,7 +37,7 @@
 #include "f1ap_cu_rrc_message_transfer.h"
 #include "common/ran_context.h"
 #include "openair3/UTILS/conversions.h"
-#include "pdcp.h"
+#include "LAYER2/nr_pdcp/nr_pdcp_oai_api.h"
 
 /*
     Initial UL RRC Message Transfer