driver/fsl_debug_server: Fix the DDR hide logic for LS2085a

This patch fixes the DDR hide logic for LS2085a, correcting the way
the Debug Server FW and MC FW images are placed on the top of system
DDR and how the rest of the system DDR space is made visibile to Linux.

Signed-off-by: Bhupesh Sharma <bhupesh.sharma at freescale.com>
Signed-off-by: Prabhakar Kushwaha <prabhakar at freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>