koji_hub: try and make sure that making srpms from scm doesn't happen on s390x

The s390x boxes have been really slow of late and have i/o issues.
Lets make sure that we only use x86 and ppc64le hosts for this so to
avoid moving large srpms around.

Signed-off-by: Kevin Fenzi <kevin@scrye.com>

roles/koji_hub/templates/hub.conf.j2

@@ -122,7 +122,7 @@ tag =
     all :: allow
 
 channel =
-    method newRepo distRepo :: use createrepo
+    method newRepo distRepo buildSRPMFromSCM :: use createrepo
     method buildContainer :: use container
     has req_channel && has_perm customchannel :: req
 
@@ -142,7 +142,7 @@ channel =
 # set this package to use the 'heavybuilder' channel. Note that this is NOT good for most anything.
 # It just happens to be for this particular package. Please check before adding anything here, you could
 # cause it to end up building a lot slower.
-    source */chromium* :: use heavybuilder
+    source */chromium :: use heavybuilder
 
     is_child_task :: parent
     all :: use default