Revert "drm/amdgpu: Ensure the DMA engine is deactivated during set ups"

This reverts commit b992a190.

This causes regression in GPU reset related test.

Cc: Alexander Deucher <Alexander.Deucher@amd.com>
Cc: ricetons@gmail.com
Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>