arm: mach-k3: Move DRAM address of ATF for AM62/AM62a

The current address of TF-A in DRAM is just below the 512MB address line.
This means if the DRAM in a system is 512MB then TF-A is right at the
end of memory which is often reused, for instance U-Boot relocates itself
here. If a system has less than 512MB then that system wouldn't work at
all as TF-A would fail to load.

To avoid the issues above, move TF-A to the start of DRAM, which doesn't
change from system to system.

As TF-A is position independent, this has no dependency on TF-A. We
also fixup DT as needed when TF-A address is moved, so this change also
has no dependency on Linux and is fully forward/backward compatible.

Signed-off-by: Andrew Davis <afd@ti.com>
Acked-by: Bryan Brattlof <bb@ti.com>