imx8m: Add DDR4 DVFS support

Add DDR4 DVFS support for i.MX8M. Currently, only tested on i.MX8MM.

Signed-off-by: Bai Ping <ping.bai@nxp.com>
(cherry picked from commit 058a759ffed26797314bc0a52db3c440240fa6a5)
4 files changed