i915/guc: Reset engine utilization buffer before registration

On GT reset, we store total busyness counts for all engines and
re-register the utilization buffer with GuC. At that time we should
reset the buffer, so that we don't get spurious busyness counts on
subsequent queries.

To repro this issue, run igt@perf_pmu@busy-hang followed by
igt@perf_pmu@most-busy-idle-check-all for a couple iterations.

Fixes: 77cdd054 ("drm/i915/pmu: Connect engine busyness stats from GuC to pmu")
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241127174006.190128-2-umesh.nerlige.ramappa@intel.com