powerpc/83xx: mpc836x_mds: add support for the nor flash

This patch adds the localbus node, moves the bcsr node into the
localbus node, and adds the flash node.

Also enable MTD support in the defconfig.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>