drm/xe: Convert GuC Engine print to snapshot capture and print.

drm/xe: Convert GuC Engine print to snapshot capture and print.

The goal is to allow for a snapshot capture to be taken at the time
of the crash, while the print out can happen at a later time through
the exposed devcoredump virtual device.

v2: Handle memory allocation failures. (Matthew)
Do not use GFP_ATOMIC on cases like debugfs prints. (Matthew)
v3: checkpatch
v4: pending_list allocation needs to be atomic because of the
    spin_lock. (Matthew)
    get back to GFP_ATOMIC only. (lockdep).

Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>