The following patch makes PPC601_SYNC_FIX depend on PPC_PMAC || PPC_PREP.
It used to depend on ALL_PPC I believe, but this was (at least
semi-intentionally I gather) backed out. The last time this was discussed,
the only platforms old enough to have a 601 to support were pmacs and
preps, so it makes some sense to only ask for these machines.