drm/xe: Introduce the wedged_mode debugfs

drm/xe: Introduce the wedged_mode debugfs

So, the wedged mode can be selected per device at runtime,
before the tests or before reproducing the issue.

v2: - s/busted/wedged
    - some locking consistency

v3: - remove mutex
    - toggle guc reset policy on any mode change

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240423221817.1285081-4-rodrigo.vivi@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>