[OpenMP][Offload] Update the Logic for Configuring Auto Zero-Copy (llvm#143638)

Summary:

Currently the Auto Zero-Copy is enabled by checking every initialized
device to ensure that no dGPU is attached to an APU. However, an APU is
designed to comprise a homogeneous set of GPUs, therefore, it should be
sufficient to check any device for configuring Auto Zero-Copy. In this
PR, it checks the first initialized device in the list.

The changes in this PR are to clearly reflect the design and logic of
enabling the feature for further improving the readibility.

Author: Kewen12

offload/libomptarget/PluginManager.cpp

@@ -286,16 +286,16 @@ void PluginManager::registerLib(__tgt_bin_desc *Desc) {
   }
   PM->RTLsMtx.unlock();
 
-  bool UseAutoZeroCopy = Plugins.size() > 0;
+  bool UseAutoZeroCopy = false;
 
   auto ExclusiveDevicesAccessor = getExclusiveDevicesAccessor();
-  for (const auto &Device : *ExclusiveDevicesAccessor)
-    UseAutoZeroCopy &= Device->useAutoZeroCopy();
+  // APUs are homogeneous set of GPUs. Check the first device for
+  // configuring Auto Zero-Copy.
+  if (ExclusiveDevicesAccessor->size() > 0) {
+    auto &Device = *(*ExclusiveDevicesAccessor)[0];
+    UseAutoZeroCopy = Device.useAutoZeroCopy();
+  }
 
-  // Auto Zero-Copy can only be currently triggered when the system is an
-  // homogeneous APU architecture without attached discrete GPUs.
-  // If all devices suggest to use it, change requirement flags to trigger
-  // zero-copy behavior when mapping memory.
   if (UseAutoZeroCopy)
     addRequirements(OMPX_REQ_AUTO_ZERO_COPY);