[CICD] Add 'gitlab-ci.yml' and '.gitlab-ci' submodule

This commit allows to enable CI/CD automation steps for this branch. In
turn they allow to automatically integrate 'linux-seco-imx' modifications
inside dedicated SRCREV.conf file in 'meta-seco-imx' repository.

.gitignore

@@ -100,6 +100,8 @@ modules.order
 !.get_maintainer.ignore
 !.gitattributes
 !.gitignore
+!.gitlab-ci
+!.gitlab-ci.yml
 !.kunitconfig
 !.mailmap
 !.rustfmt.toml

.gitlab-ci @ eee2e5d8

+Subproject commit eee2e5d82e58d8ce9d576747f1449c00fc88897f

.gitlab-ci.yml

+---
+# ---------------------------------------------------------------------------------------
+# Include the default CI steps from the gitlab-ci repo
+# ---------------------------------------------------------------------------------------
+include:
+  - project: '${CI_PROJECT_ROOT_NAMESPACE}/infrastructure/gitlab-ci'
+    ref: eee2e5d82e58d8ce9d576747f1449c00fc88897f
+    file: 'layers-integration.yml'
+
+variables:
+  GITLAB_CI_REVISION: eee2e5d82e58d8ce9d576747f1449c00fc88897f
+  BB_RECIPE_NAME: linux-seco

.gitmodules

+[submodule ".gitlab-ci"]
+	path = .gitlab-ci
+	url = ../../../infrastructure/gitlab-ci