[PATCH] ppc64: Fix oprofile when compiled as a module

My recent changes to oprofile broke it when built as a module. Fix it by
using an enum instead of a function pointer. This way we still retain
the oprofile configuration in the cputable.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>