spi: xilinx: Add new compatible strings

Add xlnx,xps-spi-2.00.a/b which is compatible string
listed in the Linux kernel.
Remove origin one which has no real background.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>