drm: drop modeset_lock_all from drm_state_info

If we push the locks down we don't have to take them all at the same
time.

Aside: Making dump_info fully safe should be fairly simple, if we
protect the ->state pointers with rcu. Simply putting a
synchronize_rcu() into the drm_atomic_state free function should be
all that's roughly needed. Well except we shouldn't block in there, so
better to put that into a work_struct. But I've not set out to fix
that little issue.

Cc: Rob Clark <robdclark@gmail.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170403083304.9083-6-daniel.vetter@ffwll.ch