nouveau: bring back legacy mmap handler

nouveau userspace back at 1.0.1 used to call the X server
DRIOpenDRMMaster interface even for DRI2 (doh!), this attempts
to map the sarea and fails if it can't.

Since 884c6dabb0eafe7227f099c9e78e514191efaf13 from Daniel,
this fails, but only ancient drivers would see it.

Revert the nouveau bits of that fix.

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: <stable@vger.kernel.org>  # 3.18
Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --cc drivers/gpu/drm/nouveau/nouveau_ttm.c
Simple merge