drm/nouveau: fix m2mf copy to tiled gart

Commit de7b7d59 introduced tiled GART, but a linear copy is
still performed. This may result in errors on eviction, fix it by
checking tiling from memtype.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Cc: stable@vger.kernel.org #3.10+
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>