drm/i915/guc: Asynchronous flush of GuC log regions

Both error-capture and relay-logging mechanism use the GuC
log infrastructure. That means the KMD must send a log flush
complete notification back to GuC after reading the data out.
This call is currently being sent synchronously.
However, synchronous H2Gs cause problems when the system is
backed up. There is no need for this to be synchronous. The
KMD wasn't even looking at the return status from it. So make
it asynchronous and then there is no issue about time outs.

Signed-off-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220607002314.1451656-2-alan.previn.teres.alexis@intel.com