spi: Revert "spi/xilinx: Remove iowrite/ioread wrappers"

This reverts commit 99082eab63449f9dfa83d5157fa6d78bfc1b04d7 since it
breaks the build due to differing implementations of iowrite() and
ioread().

Signed-off-by: Mark Brown <broonie@kernel.org>

diff --cc drivers/spi/spi-xilinx.c
Simple merge