drm/amdgpu: fix IB test MCBP bug

1)for gfx IB test we shouldn't insert DE meta data

2)we should make sure IB test finished before we
send event 3 to hypervisor otherwise the IDLE from
event 3 will preempt IB test, which is not designed
as a compatible structure for MCBP

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>