Update MPC8544 DS config

* Removed HAS_ETH2/HAS_ETH3 - MPC8544 only has TSEC1/2
* Removed some misc environment setup
* Moved to using fdtfile & fdtaddr as fdt env var names
* Enabled CONFIG_CMDLINE_EDITING

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>