vars: Add "tfgit" procedural module to abstract Git operations

Immediate usecase: we clone tf-m-ci-scripts repo in many places, with
fairly complex parameters, so there's a lot of duplication, and updating
all occurrences is time consuming and error prone. So, let's factor out
that operation into a single function.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I7efb2e5bc7ec8c690eca5a114d6e48cb68ec3559
2 files changed