drm/amdgpu: defer cmd/fence/fw buffers destroy on hw_init failure

As the cleanup jobs performed in pre_fini may still need these
buffers. NULL pointer dereference will be triggered without them.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>