powerpc/mpc85xx: socrates: add MTD partitioning support

setup MTD partitioning through mtdparts variable
and set it to:

mtdparts=fe0000000.nor:13312k(system1),13312k(system2),5120k(data),128k(env),128k(env-red),768k(u-boot)

and pass this to linux per kernel commandline.

Signed-off-by: Heiko Schocher <hs@denx.de>