[POWERPC] cell: pm_rtas_activat_signals routine cleanup

The code was setting up the debug bus for group 21 when profiling on the
event PPU CYCLES.  The debug bus is not actually used by the hardware
performance counters when counting PPU CYCLES.  Setting up the debug bus
for PPU CYCLES causes signal routing conflicts on the debug bus when
profiling PPU cycles and another PPU event.  This patch fixes the code to
only setup the debug bus to route the performance signals for the non
PPU CYCLE events.

Signed-off-by: Maynard Johnson <mpjohn@us.ibm.com>
Signed-off-by: Carl Love <carll@us.ibm.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>