imx-drm: ipuv3-crtc: change display enable/disable order

Now that ipu_dc_disable_channel correctly waits for the channel to finish,
we can reorder the enable/disable order to first stop the DC and DI and
only then disable the IDMAC. Enabling is done the other way around: IDMAC
first, then DC, then DI.

This avoids an issue where sometimes the channel would not correctly start,
leading to non-working LVDS displays.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>