powerpc/85xx: p1022ds: disable the NAND flash node if video is enabled

The Freescale P1022 has a unique pin muxing "feature" where the DIU video
controller's video signals are muxed with 24 of the local bus address signals.
When the DIU is enabled, the bulk of the local bus is disabled, preventing
access to memory-mapped devices like NAND flash and the pixis FPGA.

Therefore, if the DIU is going to be enabled, then memory-mapped devices on
the localbus, like NAND flash, need to be disabled.

This patch is similar to "powerpc/85xx: p1022ds: disable the NOR flash node
if video is enabled", except that it disables the NAND flash node instead.
This PIXIS node needs to remain enabled because it is used by platform code
to switch into indirect mode.

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