drm/xe: Rename xe_ggtt_node related functions

Bring some consistency and prepare for more xe_ggtt_node related
functions to be introduced.

Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240821193842.352557-6-rodrigo.vivi@intel.com


Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>