Added 32-bit support for the zynqmp.

The Zynq UltraScale+ MPSoC (PLAT zynqmp) is a Multi-Processor SOC
made by Xilinx that has a quad-core Cortex-A53, a dual-core Cortex-R5
and an FPGA.

This adds 32-bit, single-core support on the the Cortex-A53 cluster.