MAINTAINERS: drm/ci: xfails: add entry for panfrost

DRM CI tests panfrost drivers, and track of which tests
are failing, flaking or being skipped by the ci in the
expectations files. So add entry for these files, so
that the corresponding driver maintainer can be notified
when they change.

Signed-off-by: Vignesh Raman <vignesh.raman@collabora.com>