drm/xe: Add GTs under respective tile sysfs

With the separation of xe_tile and xe_gt, We now consider
a PCI device (xe_device) to contain one or more tiles (struct xe_tile).
Each tile will contain one or more GTs (struct xe_gt).
So lets align sysfs paths accordingly.

TODO: Currently we have gt0 under tile0 and gt1 under tile1
on multi-tile. This GT indexing still under discussion, when
it is concluded we need to revisit this change.

Reviewed-by: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>