drm/ci: generate testlist from build

Stop vendoring the testlist into the kernel. Instead, use the
testlist from the IGT build to ensure we do not miss renamed
or newly added tests.

Signed-off-by: Vignesh Raman <vignesh.raman@collabora.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Acked-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Helen Koike <helen.koike@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240529024049.356327-4-vignesh.raman@collabora.com