drm/amdgpu: Mark KFD VRAM allocations for wipe on release

Memory used by KFD applications can contain sensitive information that
should not be leaked to other processes. The current approach to prevent
leaks is to clear VRAM at allocation time. This is not effective because
memory can be reused in other ways without being cleared. Synchronously
clearing memory on the allocation path also carries a significant
performance penalty.

Stop clearing memory at allocation time. Instead mark the memory for
wipe on release.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>