drm/xe/guc: Add a helper function for dumping GuC log to dmesg

Create a helper function that can be used to dump the GuC log to dmesg
in a manner that is reliable for extraction and decode. The intention
is that calls to this can be added by developers when debugging
specific issues that require a GuC log but do not allow easy capture
of the log - e.g. failures in selftests and failues that lead to
kernel hangs.

Also note that this is really a temporary stop-gap. The aim is to
allow on demand creation and dumping of devcoredump captures (which
includes the GuC log and much more). Currently this is not possible as
much of the devcoredump code requires a 'struct xe_sched_job' and
those are not available at many places that might want to do the dump.

v2: Add kerneldoc - review feedback from Michal W.

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Julia Filipchuk <julia.filipchuk@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241003004611.2323493-12-John.C.Harrison@Intel.com