drm/xe: Add a reason string to the devcoredump

There are debug level prints giving more information about the cause
of the hang immediately before core dumps are created. However, not
everyone has debug level prints enabled or saves the dmesg log at all.
So include that information in the dump file itself. Also, at least
one of those prints included the pid as well as the process name. So
include that in the capture too.

v2: Fix kvfree vs kfree and missing kernel-doc (review feedback from
Matthew Brost)
v3: Use GFP_ATOMIC instead of GFP_KERNEL.

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241128210824.3302147-2-John.C.Harrison@Intel.com