drm/atomic-helper: Add NO_DISABLE_AFTER_MODESET flag support for plane commit

Drivers may set the NO_DISABLE_AFTER_MODESET flag in the 'flags' parameter
of the helper drm_atomic_helper_commit_planes() if the relevant display
controllers(e.g., IPUv3 for imx-drm) require to disable a CRTC's planes
when the CRTC is disabled. The helper would skip the ->atomic_disable
call for a plane if the CRTC of the old plane state needs a modesetting
operation. Of course, the drivers need to disable the planes in their CRTC
disable callbacks since no one else would do that.

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/1472461923-14364-1-git-send-email-gnuiyl@gmail.com