drm: Add initial ci/ subdirectory

And use it to store expectations about what the DRM drivers are
supposed to pass in the IGT test suite.

Also include a configuration file that points to the out-of-tree CI
scripts.

By storing the test expectations along the code we can make sure both
stay in sync with each other, and so we can know when a code change
breaks those expectations.

This will allow all contributors to drm to reuse the infrastructure
already in gitlab.freedesktop.org to test the driver on several
generations of the hardware.

v2:
  - Fix names of result expectation files to match SoC
  - Don't execute tests that are going to skip on all boards

v3:
  - Remove tracking of dmesg output during test execution

v4:
  - Move up to drivers/gpu/drm
  - Add support for a bunch of other drivers
  - Explain how to incorporate fixes for CI from a
    ${TARGET_BRANCH}-external-fixes branch
  - Remove tests that pass from expected results file, to reduce the
    size of in-tree files
  - Add docs about how to deal with outages in automated testing labs
  - Specify the exact SHA of the CI scripts to be used

v5:
  - Remove unneeded skips from Meson expectations file
  - Use a more advanced runner that detects flakes automatically
  - Use a more succint format for the expectations
  - Run many more tests (and use sharding to finish in time)
  - Use skip lists to avoid hanging machines
  - Add some build testing
  - Build IGT in each pipeline for faster uprevs
  - List failures in the GitLab UI

v6:
  - Rebase on top of latest drm-next
  - Lower priority of LAVA jobs to not impact Mesa CI as much
  - Update docs

v7:
  - Rebase on top of latest drm-next

v8:
  - Move all files specific to testing the kernel into the kernel tree
    (thus I have dropped the r-bs I had collected so far)
  - Uprev Gitlab CI infrastructure scripts to the latest from Mesa
  - Add MAINTAINERS entry
  - Fix boot on MT8173 by adding some Kconfigs that are now needed
  - Link to the docs from index.rst and hard-wrap the file

v9:
  - Only automatically run the pipelines for merge requests
  - Switch to zstd for the build artifacts to align with Mesa
  - Add Qcom USB PHYs to config as they are now =m in the defconfig

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>