drm/xe/sa: Avoid caching GGTT address within the manager

drm/xe/sa: Avoid caching GGTT address within the manager

Non-virtualized resources require fixups after SRIOV VF migration.
Caching GGTT references rather than re-computing them from the
underlying Buffer Object is something we want to avoid, as such
code would require additional fixup step and additional locking
around all the places where the address is accessed.

This change removes the cached GPU address from the Sub-Allocation
Manager, and introduces a function which recomputes and returns
the address instead.

v2: renamed xe_sa_manager_gpu_addr(), added kerneldoc

Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://lore.kernel.org/r/20250802031045.1127138-2-tomasz.lis@intel.com
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>