Move radio CMakeLists.txt to subdirectory

- move following radios: AW2S, BladeRF, IRIS, LMSSDR, RFsimulator, USRP
- move following transports: Ethernet, benetel4g, benetel5g
- for each: create independent cmake variable to switch compilation
  on/off, in order: OAI_AW2S, OAI_BLADERF, OAI_IRIS, OAI_LMSSDR,
  OAI_SIMU, OAI_USRP, OAI_ETHERNET, OAI_BENETEL4G, OAI_BENETEL5G
- Remove RF_BOARD variable, allows to compile multiple boards at once
- where applicable: remove USERSPACE/LIB in path, i.e., move files up to
  directories, as all are userspace libraries

Note that with the above, it is now mandatory to enable a radio
implementation before compiling it, e.g., for USRP:

./build_oai -w USRP
cmake .. -DOAI_USRP=ON && ninja oai_usrpdevif

cmake_targets/build_oai

@@ -282,19 +282,27 @@ function main() {
             case "$2" in
                 "USRP" | "BLADERF" | "LMSSDR" | "IRIS" | "SIMU" | "AW2SORI")
                     HW="OAI_"$2
+                    CMAKE_CMD="$CMAKE_CMD -DOAI_$2=ON"
                     ;;
                 "None")
                     HW="None"
                     ;;
                 *)
-                    echo_fatal "Unknown HW type $HW: exit..."
+                    echo_fatal "Unknown HW type $2: exit..."
             esac
-            echo_info "Setting hardware to: $HW"
-            #CMAKE_CMD="$CMAKE_CMD -DRF_BOARD=\"${HW}\""
-            CMAKE_CMD="$CMAKE_CMD -DRF_BOARD=${HW}"
             shift 2;;
        -t | --transport)
-	    TP=$2
+            case "$2" in
+              "Ethernet" | "benetel4g" | "benetel5g")
+                TP=$2
+                CMAKE_CMD="$CMAKE_CMD -DOAI_${2^^}=ON" # ^^ makes uppercase
+                ;;
+              "None")
+                HW="None"
+                ;;
+              *)
+                echo_fatal "Unknown TP type $2; exit..."
+            esac
             shift 2;;
        -P | --phy_simulators)
             SIMUS_PHY=1
@@ -436,26 +444,6 @@ function main() {
       fi
   fi
 
-  ########################################################
-  # Check validity of HW and TP parameters for eNB / gNB #
-  ########################################################
-  # to be discussed
-  
-  if [ "$eNB" = "1" -o "$gNB" = "1" ] ; then
-      if [ "$HW" = "None" -a  "$TP" = "None" ] ; then
-	      echo_info "No local radio head and no transport protocol selected"
-      fi
-      if [ "$HW" = "None" ] ; then 
-	      echo_info "No radio head has been selected (HW set to $HW)"	
-      fi
-      if [ "$TP" = "None" ] ; then
-	      echo_info "No transport protocol has been selected (TP set to $TP)"	
-      fi
-  fi
-
-  echo_info "RF HW set to $HW" 
-  # If the user doesn't specify the Linux scheduler to use, we set a value
-
   #######################################################
   # Setting and printing OAI envs, we should check here #
   #######################################################