fix(zynqmp): move bl31 with DEBUG=1 back to OCM

By default placing bl31 to addrexx 0x1000 is not good. Because this
location is used by U-Boot SPL. That's why move TF-A back to OCM where it
should be placed. BL31_BASE address exactly matches which requested address
for U-BOOT SPL boot flow.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Change-Id: I608c1b88baffec538c6ae528f057820e34971c4c