drm/imx: atomic phase 1: Use transitional atomic CRTC and plane helpers

Use the drm_plane_helper_update/disable() and drm_helper_crtc_mode_set()
transitional atomic helpers.  The crtc->mode_set_nofb callback is added
so that the primary plane is no longer tied to the CRTC.  Check/update
logics are separated to make sure crtc->mode_set_nofb and plane->atomic_update
are always successful.  Also, some necessary logics are tweaked for a smooth
transition.

Signed-off-by: Liu Ying <gnuiyl@gmail.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

drivers/gpu/ipu-v3/ipu-di.c

@@ -572,9 +572,6 @@ int ipu_di_init_sync_panel(struct ipu_di *di, struct ipu_di_signal_cfg *sig)
 	dev_dbg(di->ipu->dev, "disp %d: panel size = %d x %d\n",
 		di->id, sig->mode.hactive, sig->mode.vactive);
 
-	if ((sig->mode.vsync_len == 0) || (sig->mode.hsync_len == 0))
-		return -EINVAL;
-
 	dev_dbg(di->ipu->dev, "Clocks: IPU %luHz DI %luHz Needed %luHz\n",
 		clk_get_rate(di->clk_ipu),
 		clk_get_rate(di->clk_di),