ppc4xx: Fixup chip-selects in dtb for NAND-booting Sequoia

ppc4xx: Fixup chip-selects in dtb for NAND-booting Sequoia

Currently the NOR & NAND support in Linux only works for the "standard"
Sequoia, the version booting for NOR flash. The NAND-booting version
has the chip-selects swapped. Here the chip-select mappings:

"Standard" NOR-booting version:
CS0	NOR
CS3	NAND

NAND-booting version:
CS0	NAND
CS3	NOR

With this path the dtb gets fixed-up, so that the correct chip-select
numbers are patched in the dtb enabling correct NOR & NAND support
in Linux on the NAND-booting Sequoia version.

Signed-off-by: Stefan Roese <sr@denx.de>