drm/xe: Disable timestamp WA on VFs

drm/xe: Disable timestamp WA on VFs

The timestamp WA does not work on a VF because it requires reading MMIO
registers, which are inaccessible on a VF. This timestamp WA confuses
LRC sampling on a VF during TDR, as the LRC timestamp would always read
as 1 for any active context. Disable the timestamp WA on VFs to avoid
this confusion.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Fixes: 617d824c5323 ("drm/xe: Add WA BB to capture active context utilization")
Link: https://patch.msgid.link/20260110012739.2888434-7-matthew.brost@intel.com
(cherry picked from commit efffd56e4bd894e0935eea00e437f233b6cebc0d)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>