feat(imx8m): enable the csu init on imx8m

Enable the CSU init on i.MX8M SoC family. The 'csu_cfg' array
is just a placeholder for now as example with limited config listed.
In real use case,user can add the CSU config as needed based on system design.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Change-Id: I1f7999efa346f18f6625ed8c478d088ed75f7833