Update memory allocation guide in using pool apis

This is to allow allocations in system memory that exceed sizes
reported by a CPU device

Change-Id: I3d10d192aafcefbe4107f69b7c5e30bf7f836619


[ROCm/ROCR-Runtime commit: 3201f68f72]

projects/rocr-runtime/runtime/hsa-runtime/core/inc/amd_memory_region.h

@@ -175,6 +175,9 @@ class MemoryRegion : public core::MemoryRegion {
 
   size_t max_single_alloc_size_;
 
+  // Used to collect total system memory
+  static size_t max_sysmem_alloc_size_;
+
   HSAuint64 virtual_size_;
 
   mutable KernelMutex access_lock_;