Regression on gfx8 with ring init

[Tom St Denis]

This commit:

[root at raven linux]# git bisect good
9b0df0937a852d299fbe42a5939c9a8a4cc83c55 is the first bad commit
commit 9b0df0937a852d299fbe42a5939c9a8a4cc83c55
Author: Christian König <christian.koenig at amd.com>
Date:   Tue Sep 18 10:38:09 2018 +0200

     drm/amdgpu: remove fence fallback

     DC doesn't seem to have a fallback path either.

     So when interrupts doesn't work any more we are pretty much busted no
     matter what.

     Signed-off-by: Christian König <christian.koenig at amd.com>
     Reviewed-by: Chunming Zhou <david1.zhou at amd.com>

Results in this:

[   24.334025] [drm] Initialized amdgpu 3.27.0 20150101 for 0000:07:00.0 
on minor 1
[   24.335674] modprobe (3895) used greatest stack depth: 12600 bytes left
[   26.272358] [drm:gfx_v8_0_ring_test_ib [amdgpu]] *ERROR* amdgpu: IB 
test timed out.
[   26.272460] [drm:amdgpu_ib_ring_tests [amdgpu]] *ERROR* amdgpu: 
failed testing IB on ring 9 (-110).
[   26.407885] [drm:process_one_work] *ERROR* ib ring test failed (-110).
[   28.506708] fuse init (API version 7.27)

On init with my polaris/raven1 system.

Cheers,
Tom