drm/xe: Move debugfs GT attributes under tile directory

While in sysfs we are correctly trying to reflect the hardware
architecture and we expose GT attributes in per tile hierarchy,
in debugfs we expose GT attributes at flat level, without tiles.

Create debugfs directories to represent each tile and move GT
attributes under matching parent tile directory. To not break
existing debugfs tools, create symlink under old location:

 /sys/kernel/debug/dri/0000:00:02.0/
 ├── ...
 ├── gt0 -> tile0/gt0
 ├── gt1 -> tile0/gt1
 ├── tile0
 │   ├── gt0
 │   │   ├── ...
 │   ├── gt1
 │   │   ├── ...

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/20250714193645.763-1-michal.wajdeczko@intel.com