misc: imx8: scu: use platdata instead of priv data

priv data has not been allocated when doing bind, so it is
wrong to use dev_get_priv in bind call back.

Let's switch to use platdata in the driver to fix the issue.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Simon Glass <sjg@chromium.org>