powerpc/85xx: add ngPIXIS FPGA device tree node to the P1022DS board

The device tree for Freescale's P1022DS reference board is missing the node
for the ngPIXIS FPGA.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>