drm/xe: Pass down drm_exec context to validation

drm/xe: Pass down drm_exec context to validation

We want all validation (potential backing store allocation) to be part
of a drm_exec transaction. Therefore add a drm_exec pointer argument
to xe_bo_validate() and ___xe_bo_create_locked(). Upcoming patches
will deal with making all (or nearly all) calls to these functions
part of a drm_exec transaction. In the meantime, define special values
of the drm_exec pointer:

XE_VALIDATION_UNIMPLEMENTED: Implementation of the drm_exec transaction
has not been done yet.
XE_VALIDATION_UNSUPPORTED: Some Middle-layers (dma-buf) doesn't allow
the drm_exec context to be passed down to map_attachment where
validation takes place.
XE_VALIDATION_OPT_OUT: May be used only for kunit tests where exhaustive
eviction isn't crucial and the ROI of converting those is very
small.

For XE_VALIDATION_UNIMPLEMENTED and XE_VALIDATION_OPT_OUT there is also
a lockdep check that a drm_exec transaction can indeed start at the
location where the macro is expanded. This is to encourage
developers to take this into consideration early in the code
development process.

v2:
- Fix xe_vm_set_validation_exec() imbalance. Add an assert that
  hopefully catches future instances of this (Matt Brost)
v3:
- Extend to psmi_alloc_object

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com> #v3
Link: https://lore.kernel.org/r/20250908101246.65025-2-thomas.hellstrom@linux.intel.com