imx8mp: Remove parts MIMX8ML7 and MIMX8ML5 support

Latest datasheet revE has removed MIMX8ML7D/5D/7C/5C parts, so
update u-boot to remove decoding and support for those parts.

Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>