drm/amdgpu: remove unsafe optimization to drop preamble ib

drm/amdgpu: remove unsafe optimization to drop preamble ib

[ Upstream commit 7d9c70d23550eb86a1bec1954ccaa8d6ec3a3328 ]

Take the situation with gfxoff, the optimization may cause
corrupt CE ram contents. In addition emit_cntxcntl callback
has similar optimization which firmware can handle properly
even for power feature.

Signed-off-by: Jiansong Chen <Jiansong.Chen@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>