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

drm/xe: Convert Xe HW 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: Addressing these Matthew comments:
    - Handle memory allocation failures.
    - Do not use GFP_ATOMIC on cases like debugfs prints.
    - placement of @reg doc.
    - identation issues.
v3: checkpatch
v4: Rebase and get back to GFP_ATOMIC only.

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