drm/xe/guc: Copy GuC log prior to dumping

Add an extra stage to the GuC log print to copy the log buffer into
regular host memory first, rather than printing the live GPU buffer
object directly. Doing so helps prevent inconsistencies due to the log
being updated as it is being dumped. It also allows the use of the
ASCII85 helper function for printing the log in a more compact form
than a straight hex dump.

v2: Use %zx instead of %lx for size_t prints.
v3: Replace hexdump code with ascii85 call (review feedback from
Matthew B). Move chunking code into next patch as that reduces the
deltas of both.
v4: Add a prefix to the ASCII85 output to aid tool parsing.

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/20241003004611.2323493-6-John.C.Harrison@Intel.com