Enable IPC DMA buf

Set HSA_ENABLE_IPC_MODE_LEGACY off (i.e. use DMA bufs implementation
by default).

Change-Id: I7b1c6cb7d19310adf6f0bfe060736f4adbf7adc2

runtime/hsa-runtime/core/util/flag.h

@@ -219,7 +219,7 @@ class Flag {
     enable_mwaitx_ = (var == "1") ? true : false;
 
     var = os::GetEnvVar("HSA_ENABLE_IPC_MODE_LEGACY");
-    enable_ipc_mode_legacy_ = (var == "1") ? true : true; // Temporarily always enable
+    enable_ipc_mode_legacy_ = (var == "1") ? true : false;
 
     // Temporary environment variable to disable CPU affinity override
     // Will either rename to HSA_OVERRIDE_CPU_AFFINITY later or remove completely.