drm/atomic-helper: Disable appropriate planes in disable_planes_on_crtc()

drm/atomic-helper: Disable appropriate planes in disable_planes_on_crtc()

Currently, the helper drm_atomic_helper_disable_planes_on_crtc() calls
->atomic_disable for all planes _to be_ enabled on a particular CRTC.
This is obviously wrong for those planes which are not scanning out frames
when the helper is called.  Instead, it's sane to disable active planes
of old_crtc_state in the helper.

Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Peter Senna Tschudin <peter.senna@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Liu Ying <gnuiyl@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1472196644-30563-3-git-send-email-gnuiyl@gmail.com