MLK-21219 plat: imx8m: fix the ddr4 retention hang

Fix the ddr4 retention exit hang caused by improper
init flow.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
(cherry picked from commit ae126e71754c9c1ff758d2b12ff74e3d3f5680b9)
1 file changed