arm: fsl: csu: Reduce size of ns_dev

None of the values in this struct are larger than 256, so we can reduce
the members to u8s. This saves around 1K.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>