drm/xe/pm: Hold the validation lock around evicting user-space bos for suspend

drm/xe/pm: Hold the validation lock around evicting user-space bos for suspend

During pm notifier eviction we may still race with validations.
Ensure those are blocked out during eviction to ensure we have
access to as much system memory as possible.

During the suspend operation itself, we run single-threaded so that
shouldn't be a problem.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://lore.kernel.org/r/20250918142848.21807-2-thomas.hellstrom@linux.intel.com