drm/xe/devcoredump: Add ASCII85 dump helper function

drm/xe/devcoredump: Add ASCII85 dump helper function

[ Upstream commit ec1455ce7e35a31289d2dbc1070b980538698921 ]

There is a need to include the GuC log and other large binary objects
in core dumps and via dmesg. So add a helper for dumping to a printer
function via conversion to ASCII85 encoding.

Another issue with dumping such a large buffer is that it can be slow,
especially if dumping to dmesg over a serial port. So add a yield to
prevent the 'task has been stuck for 120s' kernel hang check feature
from firing.

v2: Add a prefix to the output string. Fix memory allocation bug.
v3: Correct a string size calculation and clean up a define (review
feedback from Julia F).

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/20241003004611.2323493-5-John.C.Harrison@Intel.com
Stable-dep-of: 5dce85fecb87 ("drm/xe: Move the coredump registration to the worker thread")
Signed-off-by: Sasha Levin <sashal@kernel.org>