drm/amdgpu/mes: fix issue of writing to the same log buffer from 2 MES pipes

With Unified MES enabled in gfx12, need separate event log buffer for the
2 MES pipes to avoid data overwrite.

Signed-off-by: Michael Chen <michael.chen@amd.com>
Reviewed-by: Jack Xiao <Jack.Xiao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 144df260)
Cc: stable@vger.kernel.org # 6.11.x