CI: add tags to all jobs

Tag all jobs with the DEFAULT_TAG variable so each instance can control
what tags the jobs have, whilst still explicitly tagging the jobs which
need specific tags (such as x86_64 for jobs which need to run x86-only
binaries)

Signed-off-by: Ross Burton <ross.burton@arm.com>

.gitlab-ci.yml

@@ -13,6 +13,8 @@ stages:
 
 # Common job fragment to get a worker ready
 .setup:
+  tags:
+    - $DEFAULT_TAG
   stage: build
   variables:
     KAS_WORK_DIR: $CI_PROJECT_DIR/work
@@ -63,6 +65,8 @@ n1sdp/bootstrap:
 # What percentage of machines in the layer do we build
 machine-coverage:
   stage: bootstrap
+  tags:
+    - $DEFAULT_TAG
   script:
   - ./ci/check-machine-coverage
   coverage: '/Coverage: \d+/'