drm/ttm: use new move interface for known system->ttm moves

In all 3 drivers there is a case where the driver knows the
bo is in SYSTEM so don't call the api that checks that.

Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201019071314.1671485-4-airlied@gmail.com