ppc4xx: Fix FDT EBC mappings on Canyonlands

This patch fixes 2 problems with FDT EBC mappings on Canyonlands.
First, NAND EBC mapping was missing, making Linux NAND driver
unusable on this board. Second, NOR remapping code assumed that
NOR is always on CS0, however when booting from NAND NOR is on CS3.

Signed-off-by: Felix Radensky <felix@embedded-sol.com>
Signed-off-by: Stefan Roese <sr@denx.de>