drm/i915/dp: Fix the PSR debugfs entries wrt. MST connectors

drm/i915/dp: Fix the PSR debugfs entries wrt. MST connectors

MST connectors don't have a static attached encoder, as their encoder
can change depending on the pipe they use; so the encoder for an MST
connector can't be retrieved using intel_dp_attached_encoder() (which
may return NULL for MST). Most of the PSR debugfs entries depend on a
static connector -> encoder mapping which is only true for eDP and SST
DP connectors and not for MST. These debugfs entries were enabled for
MST connectors as well recently to provide PR information for them, but
handling MST connectors needs more changes.

Fix this by not adding for now the PSR entries on MST connectors. To
make things more uniform add the entries for SST connectors on all
platforms, not just on platforms supporting DP2.0.

v2:
- Keep adding the entries for SST connectors. (Jouni)
- Add a TODO: comment for MST support.

Fixes: ef75c25e8fed ("drm/i915/panelreplay: Debugfs support for panel replay")
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/9850
Cc: Animesh Manna <animesh.manna@intel.com>
Cc: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240103152609.2434100-1-imre.deak@intel.com