drm/amdgpu: disable the VRAM manager on special placements v2

This disables the VRAM manager when a special placement is requested, otherwise
we play ping/pong with the buffers on every command submission.

v2: only check lpfn

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: JimQu <Jim.Qu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>