aarch64: Exclude syslinux from ironic conductor packages

The 'syslinux' package is not available on aarch64, so it is only
included in the ironic conductor packages for x86_64 systems.

Related-Bug: #1749780
Change-Id: I3eea308a0a70e47dd3b185eece106185b25616f5
(cherry picked from commit 7b4913e)

Author: bbezak

docker/ironic/ironic-conductor/Dockerfile.j2

@@ -23,8 +23,12 @@ LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build
         'util-linux',
         'xfsprogs',
         'genisoimage',
-        'syslinux',
     ] %}
+    {% if base_arch in ['x86_64'] %}
+        {% set ironic_conductor_packages = ironic_conductor_packages + [
+            'syslinux'
+        ] %}
+    {% endif %}
 {% elif base_package_type == 'deb' %}
     {% set ironic_conductor_packages = [
         'bsdmainutils',