drm/xe: Drop unused ggtt_balloon field

drm/xe: Drop unused ggtt_balloon field

During recent GGTT refactoring we missed to drop now unused field
from the xe_tile. Drop it now.

Fixes: e904c56ba6e0 ("drm/xe: Rewrite GGTT VF initialization")
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Maarten Lankhorst <dev@lankhorst.se>
Link: https://patch.msgid.link/20260510205605.642-1-michal.wajdeczko@intel.com
(cherry picked from commit 21d5a871f57909dc4d8e4f5d3bf92f9ccf2597b2)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>