zynqmp: Do not place u-boot to reserved memory location

TF-A and SecureOS can allocate the part of DDR for self but U-Boot is not
handling this configuration that the part of memory is reserved and
shouldn't be used by U-Boot. That's why read all reserved memory locations
and don't use it.
The code was taken from commit 4a1b975d ("board: stm32mp1: reserve
memory for OP-TEE in device tree") and commit 1419e5b5 ("stm32mp:
update MMU config before the relocation") which is used by stm32 and does
the job properly.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>