drm/xe/svm: Add xe_svm_range_validate() and xe_svm_range_migrate_to_smem()

drm/xe/svm: Add xe_svm_range_validate() and xe_svm_range_migrate_to_smem()

The xe_svm_range_validate() function checks if a range is
valid and located in the desired memory region.

xe_svm_range_migrate_to_smem() checks if range have pages in devmem and
migrate them to smem.

v2
- Fix function stub in xe_svm.h
- Fix doc

v3 (Matthew Brost)
- Remove extra new line
- s/range->base.flags.has_devmem_pages/xe_svm_range_in_vram

v4 (Matthew Brost)
- s/xe_svm_range_in_vram/range->base.flags.has_devmem_pages
- Move eviction logic to separate function

Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Acked-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://lore.kernel.org/r/20250513040228.470682-12-himal.prasad.ghimiray@intel.com
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>