drm/amdgpu: use DRM_SCHED_FENCE_DONT_PIPELINE for VM updates

Make sure that we always have a CPU round trip to let the submission
code correctly decide if a TLB flush is necessary or not.

Signed-off-by: Christian König <christian.koenig@amd.com>
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/2113#note_1579296
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Luben Tuikov <luben.tuikov@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221014081553.114899-2-christian.koenig@amd.com