fix(imx8m): backup mr12/14 value from lpddr4 chip

Backup the mr12/14 value as the actual value used is not the
one we configured in the ddrc config timing.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Ye Li <ye.li@nxp.com>
Change-Id: If04733b34a3b4c080828bb7c82e83f0badbeaafd
3 files changed