arm/powerpc: setup: apply assert_msg

Signed-off-by: Andrew Jones <drjones@redhat.com>
Message-Id: <20170522181821.29482-2-drjones@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>