ansible: no arm devtoolset-6-libatomic-devel

It isn't there now, so probably doesn't have to be, and it doesn't seem
to be available, so move it out of the common packages.

PR-URL: #2262

ansible/roles/baselayout/vars/main.yml

@@ -42,11 +42,11 @@ packages: {
   # centos-release-scl is required to enable SCLo but we do it manually in
   # partials/repo/centos7.yml for arm64
   centos7_arm64: ['git'], # git2u not available for aarch64 (yet)
-  centos7_x64: ['git2u,centos-release-scl'],
-  centos7_ppc64: ['git'],
+  centos7_x64: ['devtoolset-6-libatomic-devel,git2u,centos-release-scl'],
+  centos7_ppc64: ['devtoolset-6-libatomic-devel,git'],
 
   centos7: [
-    'bzip2-devel,openssl-devel,ccache,gcc-c++,devtoolset-6,sudo,devtoolset-6-libatomic-devel,zlib-devel,libffi-devel,devtoolset-8,devtoolset-8-libatomic-devel',
+    'bzip2-devel,openssl-devel,ccache,gcc-c++,devtoolset-6,sudo,zlib-devel,libffi-devel,devtoolset-8,devtoolset-8-libatomic-devel',
   ],
 
   aix: [