feat(plat/zynqmp): extend DT description by TF-A

In case of TF-A running out of DDR there is a need to reserved
memory to let other SW know that none can't use this memory. HW
wise this region can be (and should be) also protected by
protection unit XMPU. This is the first step to add reserved
memory location to DT.

DT address corresponds with default address in U-Boot and also
default address in Xilinx BSPs.

Code is valid only when TF-A runs out of DDR. When it runs out
of OCM there is no need to reseve anything because OCM is hidden
to OS.

Change-Id: I01f230ced67207a159128cc11d11d36dd4590cab
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
3 files changed