board: ns3: limit U-boot relocation within 16MB memory

board: ns3: limit U-boot relocation within 16MB memory

By default relocation happens to a higher address of DDR,
i.e, DDR start + DDR size.

U-Boot shall be used to collect the ramdump.
Restrict U-Boot to use only the 16MB memory, so that this
memory can be reserved. Limit relocation to happen within
16MB memory, start 0xFF00_0000 and end 0x1_0000_0000

Signed-off-by: Bharat Kumar Reddy Gooty <bharat.gooty@broadcom.com>
Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>
Reviewed-by: Simon Glass <sjg@chromium.org>