rocr: Put back scratch_backing_memory_byte_size

The scratch_backing_memory_byte_size is not used by CP, but it is
currently used by rocgdb. Putting the field back, but we need to find a
solution for alt_scratch_backing_memory_byte_size.

Also, completely disabling alternate scratch as we need some changes to
support debugger.

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

@@ -154,9 +154,11 @@ class Flag {
     enable_scratch_async_reclaim_ = (var == "0") ? false : true;
 
     var = os::GetEnvVar("HSA_ENABLE_SCRATCH_ALT");
-    //Temporary: Disable alternate scratch by default as it can cause occasional hangs
-    //enable_scratch_alt_ = (var == "0") || !enable_scratch_async_reclaim_ ? false : true;
-    enable_scratch_alt_ = (var == "1") && enable_scratch_async_reclaim_ ? true : false;
+    // Temporary: Completely disable alternate scratch because we need to update
+    // the debugger so that it can tell whether a dispatch is using alternate scratch
+    // instead of main scratch
+    // enable_scratch_alt_ = (var == "0") || !enable_scratch_async_reclaim_ ? false : true;
+    enable_scratch_alt_ = false;
 
     tools_lib_names_ = os::GetEnvVar("HSA_TOOLS_LIB");