Revert of [Atomics] Remove Atomics code stubs; use TF ops

src/compiler/mips/code-generator-mips.cc

Index: src/compiler/mips/code-generator-mips.cc
diff --git a/src/compiler/mips/code-generator-mips.cc b/src/compiler/mips/code-generator-mips.cc
index c592cecd6f22ae82458feee86eafeced3d392777..453d553d8c8e28e822a1af9d2edd0dc9f69eb04d 100644
--- a/src/compiler/mips/code-generator-mips.cc
+++ b/src/compiler/mips/code-generator-mips.cc
@@ -1323,13 +1323,6 @@
     case kCheckedLoadWord64:
     case kCheckedStoreWord64:
       UNREACHABLE();  // currently unsupported checked int64 load/store.
-      break;
-    case kAtomicLoadInt8:
-    case kAtomicLoadUint8:
-    case kAtomicLoadInt16:
-    case kAtomicLoadUint16:
-    case kAtomicLoadWord32:
-      UNIMPLEMENTED();
       break;
   }
 }  // NOLINT(readability/fn_size)