mem-ruby: Add missing CPUonly check for VIPER

The CPUonly variable in MOESI_AMD_Base's Directory indicates that probes
should not be sent to any GPU SLICC controllers as they are not part of
CPU. There is one CPUonly check missing which causes problems in
GPU-only Ruby networks as there is no route to any controllers with that
MachineType. Add a condition to check CPUonly and do nothing in that
case.

Change-Id: I41b6c04feec473e34b04402adfb5978e75b847b6
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/51927
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/mem/ruby/protocol/MOESI_AMD_Base-dir.sm

@@ -654,8 +654,10 @@ machine(MachineType:Directory, "AMD Baseline protocol")
         out_msg.MessageSize := MessageSizeType:Control;
         out_msg.Destination.broadcast(MachineType:CorePair);
 
-        // add relevant TCC node to list. This replaces all TCPs and SQCs
-        if (noTCCdir) {
+        // Add relevant TCC node to list. This replaces all TCPs and SQCs
+        if (CPUonly) {
+            // CPU only has neither TCC nor TCC directory to add.
+        } else if (noTCCdir) {
           out_msg.Destination.add(mapAddressToRange(address,MachineType:TCC,
                                   TCC_select_low_bit, TCC_select_num_bits));
         } else {