spi/xilinx: fold platform_driver support into main body

This patch merges the platform driver support into the main body of
xilinx_spi.c in preparation for merging the OF and non-OF support
code.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Tested-by: Michal Simek <monstr@monstr.eu>

diff --cc drivers/spi/Kconfig
Simple merge

diff --cc drivers/spi/Makefile
Simple merge

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

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