drm/amdgpu: WARN when freeing kernel memory during suspend

When buffers are freed during suspend there is no guarantee that
they can be re-allocated during resume.

The PSP subsystem seems to be quite buggy regarding this, so add
a WARN_ON() to point out those bugs.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexdeucher@amd.com>
Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>