powerpc/mpc85xx: fixes and updates for socrates board

current mainline does not work on socrates board. To
get it back up working, there are some updates needed
in socrates_defconfig.

Signed-off-by: Heiko Schocher <hs@denx.de>
Fixes: 94633c36 ("net: Make DM_ETH be selected by NETDEVICE")
Fixes: 2f8a6db5 ("Finish conversion of CONFIG_SYS_CLK_FREQ to Kconfig")