390 really has no eieio instruction, so get rid of the implied ppc
semantics and in addition change mb() into a function.
Also remove SYNC_OTHER_CORES() since it is unused.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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