[POWERPC] 86xx: Add defconfig for Wind River SBC8641D board

This adds a sample defconfig for the Wind River SBC8641D
board, with SMP, PCI and NFS root enabled.
Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>