drm/xe: Add initial support for separate kernel VRAM region on the tile

drm/xe: Add initial support for separate kernel VRAM region on the tile

So far, kernel and userspace allocations have shared the same VRAM region.
However, in some scenarios, it may be necessary to reserve a separate
VRAM area exclusively for kernel allocations.
Let's add preliminary support for such a configuration.

v2:
- replaced for_each_bo_flag_vram with the improved
  for_each_set_bo_vram_flag helper (Matthew)
- moved the VRAM flag iteration macro definition into xe_bo.c (Matthew)
- drop unused bo_flgas from bo_vram_flags_to_vram_placement (Matthew)
- use hweight32 helper in __xe_bo_fixed_placement for readability
  (Matthew)
v3: remove unnecessary VRAM fixup id

Signed-off-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://lore.kernel.org/r/20251003162619.1984236-2-piotr.piorkowski@intel.com