drm/xe/guc: Dump entire CTB on errors

The dump of the CT buffers was only showing the unprocessed data which
is not generally useful for saying why a hang occurred - because it
was probably caused by the commands that were just processed. So save
and dump the entire buffer but in a more compact dump format. Also
zero fill it on allocation to avoid confusion over uninitialised data
in the dump.

v2: Add kerneldoc - review feedback from Michal W.
v3: Fix kerneldoc.
v4: Use ascii85 instead of hexdump (review feedback from Matthew B).
v5: Dump the entire CTB object rather than separately dumping just the
H2G and G2H sections. That way it includes the full header info.

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/20241003004611.2323493-10-John.C.Harrison@Intel.com