ppc4xx: Cleanup for partial linking and --gc-sections

ppc4xx: Cleanup for partial linking and --gc-sections

This commit adapts 4xx boards for partial linking with --gc-sections.

Signed-off-by: Stefan Roese <[email protected]>
Signed-off-by: Wolfgang Denk <[email protected]>
Cc: Stefan Roese <[email protected]>
Cc: Tirumala Marri <[email protected]>
Cc: David Updegraff <[email protected]>
Cc: Matthias Fuchs <[email protected]>
Cc: Dirk Eibach <[email protected]>
Cc: Larry Johnson <[email protected]>
Cc: Peter De Schrijver <[email protected]>
Cc: Niklaus Giger <[email protected]>
Cc: Daniel Poirot <[email protected]>
Acked-by: Stefan Roese <[email protected]>