drm/xe/devcoredump: Use scope-based cleanup

drm/xe/devcoredump: Use scope-based cleanup

Use scope-based cleanup for forcewake and runtime PM in the devcoredump
code.  This eliminates some goto-based error handling and slightly
simplifies other functions.

v2:
 - Move the forcewake acquisition slightly higher in
   devcoredump_snapshot() so that we maintain an easy-to-understand LIFO
   cleanup order.  (Gustavo)

Cc: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patch.msgid.link/20251118164338.3572146-41-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>