BugLink: http://bugs.launchpad.net/bugs/1768474

Upstream commits
6e179d64 ("s390: add automatic detection of the spectre defense") and
f19fbd5e ("s390: introduce execute-trampolines for branches")
added new EXPOLINE config options, so add them to the config files.
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>