drm/xe/vf: Introduce helpers to access GGTT configuration

In upcoming patch we want to separate tile-oriented VF functions
from GT-oriented functions and to allow the former access a GGTT
configuration stored at GT level we need to provide some helpers.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Tomasz Lis <tomasz.lis@intel.com>
Reviewed-by: Tomasz <Lis&lt;tomasz.lis@intel.com>
Link: https://lore.kernel.org/r/20250602103325.549-2-michal.wajdeczko@intel.com