drm: Move drm_lock_data out of drmP.h

And remove the semi-kernel-doc stuff, to make sure no one uses this.

Reviewed-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170308141257.12119-4-daniel.vetter@ffwll.ch