[POWERPC] cell: Add symbol exports for oprofile

Add symbol-exports for the new routines in arch/powerpc/platforms/cell/pmu.c.
They are needed for Oprofile, which can be built as a module.

Signed-off-by: Kevin Corry <kevcorry@us.ibm.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>