drm/xe: Unify the initialization of VRAM regions

Currently in the drivers we have defined VRAM regions per device and per
tile. Initialization of these regions is done in two completely different
ways. To simplify the logic of the code and make it easier to add new
regions in the future, let's unify the way we initialize VRAM regions.

v2:
- fix doc comments in struct xe_vram_region
- remove unnecessary includes (Jani)
v3:
- move code from xe_vram_init_regions_managers to xe_tile_init_noalloc
  (Matthew)
- replace ioremap_wc to devm_ioremap_wc for mapping VRAM BAR
  (Matthew)
- Replace the tile id parameter with vram region in the xe_pf_begin
  function.
v4:
- remove tile back pointer from struct xe_vram_region
- add new back pointers: xe and migarte to xe_vram_region

Signed-off-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Cc: Stuart Summers <stuart.summers@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com> # rev3
Acked-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250714184818.89201-6-piotr.piorkowski@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>