add allmod CI scenario

Build everything as a module. This should test build any new code.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

ci/gitlab-ci/yml/scenarios/allmod.yml

+# SPDX-License-Identifier: GPL-2.0-or-later
+
+.kernel-combinations:
+  parallel:
+    matrix:
+      - KCI_KERNEL_ARCH: "x86_64"
+        KCI_DEFCONFIG: "allmodconfig"
+
+      - KCI_KERNEL_ARCH: "arm64"
+        KCI_DEFCONFIG: "allmodconfig"
+
+      - KCI_KERNEL_ARCH: "arm"
+        KCI_DEFCONFIG: "allmodconfig"