armv8/fsl-lsch3: Support 256M mem split for MC & dbg-srvr

The agreed split of the top of memory is 256M for debug server and 256M
 for MC. This patch implements the split.

 In addition, the MC mem must be 512MB aligned, so the amount of memory
 to hide must be 512MB to achieve that alignment.

Signed-off-by: Stuart Yoder <stuart.yoder@freescale.com>
Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>