drm/xe/configfs: Rename struct xe_config_device

drm/xe/configfs: Rename struct xe_config_device

Rename it to struct xe_config_group_device to better match its
purpose. It will also help us to reintroduce in the upcoming patch
the same struct name but this time to hold only configuration data.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20250731193339.179829-6-michal.wajdeczko@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>