drm/i915/gt: use designated initializers for intel_gt_debugfs_file

drm/i915/gt: use designated initializers for intel_gt_debugfs_file

CONFIG_RANDSTRUCT may reorder structure fields, which makes positional
initializers unsafe. The i915 GT debugfs tables were using positional
initializers for `struct intel_gt_debugfs_file`, and on configs where
the layout differs (e.g., presence/absence of the `.eval` callback),
this can lead to fields being initialized incorrectly and trigger
randstruct warnings such as:

```
  drivers/gpu/drm/i915/gt/intel_gt_debugfs.c:75:51: note: randstruct:
  casting between randomized structure pointer types (constructor)
```

Switch all the GT debugfs file arrays to designated initializers. This
binds each value to the intended member regardless of structure
reordering or optional members and removes the warning while preserving
the intended initialization. Also drops the '&' from
intel_eval_slpc_support so .eval receives the function pointer directly.

No functional change, only initialization style is updated.

Signed-off-by: Sebastian Brzezinka <sebastian.brzezinka@intel.com>
Reviewed-by: Krzysztof Karas <krzysztof.karas@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://lore.kernel.org/r/bae491e8098705a87304a7c94573b377e8c8fa37.1765897826.git.sebastian.brzezinka@intel.com