Enable translations for petitboot

This change adds translations for petitboot. We already have the message
catalogues for a bunch of languages, so enable building these into the
final image.

We enable these for firestone and habanero, but there's no reason we
couldn't do this for other languages too.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
diff --git a/openpower/overlay/etc/locale b/openpower/overlay/etc/locale
index 6556836..6737e87 100644
--- a/openpower/overlay/etc/locale
+++ b/openpower/overlay/etc/locale
@@ -1 +1 @@
-LANG=en_US.utf-8
+LANG=en_US.utf8