drm/xe: Use dynamic allocation for tile and device VRAM region structures

drm/xe: Use dynamic allocation for tile and device VRAM region structures

In future platforms, we will need to represent the device and tile
VRAM regions in a more dynamic way, so let's abandon the static
allocation of these structures and start use a dynamic allocation.

v2:
 - Add a helpers for accessing fields of the xe_vram_region structure
v3:
- Add missing EXPORT_SYMBOL_IF_KUNIT for
  xe_vram_region_actual_physical_size

Signed-off-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Cc: Stuart Summers <stuart.summers@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Satyanarayana K V P <satyanarayana.k.v.p@intel.com>
Reviewed-by: Satyanarayana K V P <satyanarayana.k.v.p@intel.com>
Acked-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250714184818.89201-3-piotr.piorkowski@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>