drm/nouveau: use shared fences for readable objects

nouveau keeps track in userspace whether a buffer is being
written to or being read, but it doesn't use that information.

Change this to allow multiple readers on the same bo.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Acked-by: Ben Skeggs <bskeggs@redhat.com>

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

diff --cc drivers/gpu/drm/nouveau/nouveau_bo.h
Simple merge

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

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

diff --cc drivers/gpu/drm/nouveau/nouveau_fence.h
Simple merge

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