ARM: zynq: make use of debug_ll_io_init()

Convert low-level debugging routines to make use of debug_ll_io_init().
This is part of the preparation for ARCH_MULTIPLATFORM support for Zynq.

Signed-off-by: Josh Cartwright <josh.cartwright@ni.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>