drm/atomic: add new drm_debug bit to dump atomic state

The contents of drm_{plane,crtc,connector}_state is dumped before
commit.  If a driver extends any of the state structs, it can implement
the corresponding funcs->atomic_print_state() to add it's own driver
specific state.

Signed-off-by: Rob Clark <robdclark@gmail.com>
[seanpaul resolved conflict in drm_plane.h]
Signed-off-by: Sean Paul <seanpaul@chromium.org>