soc: imx: Read imx8mm soc revision from anatop

Like on imx6/7 we can read version information from a register in
anatop, and in the same format.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>