Revert "sunxi: Reserve ATF memory space on A64"

The ARM Trusted Firmware (ATF) code now lives in SRAM on the Pine64/A64,
so we can claim the whole of DRAM for OS use.

This reverts commit 3ffe39ed.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>