[Offload] Stop the RPC server faiilng with more than one GPU (llvm#125982)

Summary:
Pretty dumb mistake of me, forgot that this is run per-device and
per-plugin, which fell through the cracks with my testing because I have
two GPUs that use different plugins.

Author: jhuber6

offload/plugins-nextgen/common/src/PluginInterface.cpp

@@ -1269,8 +1269,9 @@ Error GenericDeviceTy::setupRPCServer(GenericPluginTy &Plugin,
   if (auto Err = Server.initDevice(*this, Plugin.getGlobalHandler(), Image))
     return Err;
 
-  if (auto Err = Server.startThread())
-    return Err;
+  if (!Server.Thread->Running.load(std::memory_order_acquire))
+    if (auto Err = Server.startThread())
+      return Err;
 
   RPCServer = &Server;
   DP("Running an RPC server on device %d\n", getDeviceId());
@@ -1895,7 +1896,7 @@ Error GenericPluginTy::deinit() {
   if (GlobalHandler)
     delete GlobalHandler;
 
-  if (RPCServer && RPCServer->Thread->Running.load(std::memory_order_relaxed))
+  if (RPCServer && RPCServer->Thread->Running.load(std::memory_order_acquire))
     if (Error Err = RPCServer->shutDown())
       return Err;