drm/xe: Avoid toggling schedule state to check LRC timestamp in TDR

drm/xe: Avoid toggling schedule state to check LRC timestamp in TDR

We now have proper infrastructure to accurately check the LRC timestamp
without toggling the scheduling state for non-VFs. For VFs, it is still
possible to get an inaccurate view if the context is on hardware. We
guard against free-running contexts on VFs by banning jobs whose
timestamps are not moving. In addition, VFs have a timeslice quantum
that naturally triggers context switches when more than one VF is
running, thus updating the LRC timestamp.

For multi-queue, it is desirable to avoid scheduling toggling in the TDR
because this scheduling state is shared among many queues. Furthermore,
this change simplifies the GuC state machine. The trade-off for VF cases
seems worthwhile.

v5:
 - Add xe_lrc_timestamp helper (Umesh)
v6:
 - Reduce number of tries on stuck timestamp (VF testing)
 - Convert job timestamp save to a memory copy (VF testing)
v7:
 - Save ctx timestamp to LRC when start VF job (VF testing)

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patch.msgid.link/20260110012739.2888434-8-matthew.brost@intel.com