[AArch64] Remove Unsupported = 1 flag for the WriteAtomic WriteRes.

In practice, this patch has no effect on scheduling.

There is no test case as there already exists a comprehensive test case for
LSE Atomics.

Patch by Stefan Teleman

Differential Revision: https://reviews.llvm.org/D40694

llvm-svn: 322291

llvm/lib/Target/AArch64/AArch64SchedThunderX2T99.td

@@ -391,7 +391,7 @@ def : WriteRes<WriteBarrier, []> { let Latency = 1; }
 def : WriteRes<WriteHint,    []> { let Latency = 1; }
 
 def : WriteRes<WriteAtomic,  []> {
-  let Unsupported = 1;
+  let Latency = 4;
   let NumMicroOps = 2;
 }