gitlab-ci: Extract EDK2 job rules to reusable section

gitlab-ci: Extract EDK2 job rules to reusable section

All jobs depending on 'docker-edk2' job must use at most all
the rules that triggers it. The simplest way to ensure that
is to always use the same rules. Extract all the rules to a
reusable section, and include this section (with the 'extends'
keyword) in both 'docker-edk2' and 'build-edk2' jobs.

The problem was introduced in commit 71920809cea ("gitlab-ci.yml:
Add jobs to build EDK2 firmware binaries"), but was revealed in
commit 1925468ddbf ("docker: EDK2 build job depends on EDK2
container") and eventually failed on CI:
https://gitlab.com/qemu-project/qemu/-/pipelines/335995843

Reported-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Message-Id: <20210714101003.3113726-1-philmd@redhat.com>