powerpc/p1022ds: add missing iounmap calls to platform file

The platform file for the Freecale P1022DS reference board is not freeing
the ioremap() mapping of the PIXIS and global utilities nodes it creates.

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