drm: Add checks for atomic_[duplicate/destroy]_state with atomic drivers

This patch add checks for atomic_[duplicate/destroy]_state of
drm_[connector/crtc/plane]_funcs for atomic drivers in the relevant
drm_*_init functions since these callback are mandatory for atomic drivers.

Update the kerneldoc comments for those callbacks.

Signed-off-by: Haneen Mohammed <hamohammed.sa@gmail.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180525012555.GA8448@haneen-vb