85xx: Fix some settings for MPC8569MDS board

- Increase the size of malloc to 512KB because MPC8569MDS needs more memory for
malloc to support up to eight Ethernet interfaces.
- Move Environment address out of uboot thus the saved environment variables
will not be erased after u-boot is re-programmed.

Signed-off-by: Haiying Wang <Haiying.Wang@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>