arm64: mvebu: do not map firmware RT service region

arm64: mvebu: do not map firmware RT service region

There is region left by ATF, which needs to remain in memory to provide RT
services. To prevent overwriting it by u-boot, do not provide any mapping
for this memory region, so any attempt to access it will trigger
synchronous exception.

Update sr 2021-04-12:
Don't update armada3700/cpu.c mmu table, as this has specific changes
included in mainline.

Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
Signed-off-by: Stefan Roese <sr@denx.de>