powerpc/4xx: Sequoia: Enable NAND support

Now that the 4xx NAND driver is available again in arch/powerpc, let's
enable it on Sequoia. This patch also disables the early debug messages
(CONFIG_PPC_EARLY_DEBUG) in the Sequoia defconfig.

Signed-off-by: Stefan Roese <sr@denx.de>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>