[PATCH 2.6.12] PPC32: Update chestnut platform files

Update Chestnut platform files.

- Set up mtd partition from arch-specific platform file and remove obsoleted mtd map.
- Update default config file (now enables embedded ethernet driver).
- Make some minor fixups.
- General code cleanup.

Please apply.

Signed-off-by: Mark A. Greer <redacted>
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