drm/fsl-dcu: do not transfer registers on plane init

There is no need to explicitly initiate a register transfer and
turn off the DCU after initializing the plane registers. In fact,
this is harmful and leads to unnecessary flickers if the DCU has
been left on by the bootloader.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Tested-By: Meng Yi <meng.yi@nxp.com>