PPC/s390: Enable atomic operation tests

Change-Id: I05bd981c8050a6f59446be660d449320979ceaea
Reviewed-on: https://chromium-review.googlesource.com/1053957Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#53168}

test/mjsunit/mjsunit.status

@@ -749,9 +749,6 @@
 ##############################################################################
 ['arch == ppc64 or arch == ppc or arch == s390 or arch == s390x', {
 
-  # TODO(ppc/s390): implement atomic operations
-  'wasm/atomics': [SKIP],
-  'wasm/shared-memory': [SKIP],
   # TODO(ppc/s390): fix constant pool issue and implement tagging for reloc
   'wasm/compiled-module-serialization': [SKIP],
   'regress/wasm/regress-808980': [SKIP],