drm/xe: Convert pinned suspend eviction for exhaustive eviction

Pinned suspend eviction and preparation for eviction validates
system memory for eviction buffers. Do that under a
validation exclusive lock to avoid interfering with other
processes validating system graphics memory.

v2:
- Avoid gotos from within xe_validation_guard().
- Adapt to signature change of xe_validation_guard().

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250908101246.65025-14-thomas.hellstrom@linux.intel.com