UPSTREAM: drm/amdgpu: cond_exec only for schedule with a job

issue:
under SR-IOV sometimes the iB test will fail on
gfx ring

fix:
with cond_exec inserted in RB the gfx engine would
skip part packets if RLCV issue PREEMPT on gfx engine
if gfx engine is prior to COND_EXEC packet, this is
okay for regular command from UMD, but for the ib test
since the whole dma format doesn't support PREEMPT
so must remove the COND_EXEC from it.

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Christian Knig <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 113890ee99575a5340ab8729b207e48aaac2eb06)

BUG=b:111106006,b:111209695
TEST=suspend_stress_test

Change-Id: I6564f275ab098256845339bac109eade80b226b2
Signed-off-by: Pratik Vishwakarma <Pratik.Vishwakarma@amd.com>
Reviewed-on: https://chromium-review.googlesource.com/1134932
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>