kernel.spec: automotive: disable kernel signature by default

JIRA: https://issues.redhat.com/browse/RHEL-78808

Upstream Status: https://gitlab.com/cki-project/kernel-ark.git

commit 12a888dc9f1f56c91f68921ca36f4d31596e0a90
Author: Eric Chanudet <echanude@redhat.com>
Date:   Fri Jun 27 16:39:24 2025 -0400

    kernel.spec: automotive: disable kernel signature by default

    Automotive only.

    With the possibility of inserting a certificate in the ring once the
    kernel is built, signing the kernel at this stage is no longer possible
    and has to be done later, namely at image composition.

    Signed-off-by: Eric Chanudet <echanude@redhat.com>

Signed-off-by: Eric Chanudet <echanude@redhat.com>

Author: eric-ch

redhat/kernel.spec.template

@@ -452,6 +452,8 @@ Summary: The Linux kernel
 %define with_kabichk 0
 %define with_kernel_abi_stablelists 0
 %define with_kabidw_base 0
+%define signkernel 0
+%define signmodules 1
 %endif