powerpc/perf: Remove PME_ prefix for power7 events

We used the PME_ prefix earlier to avoid some macro/variable name
collisions.  We have since changed the way we define/use the event
macros so we no longer need the prefix.

By dropping the prefix, we keep the the event macros consistent with
their official names.

Reported-by: Michael Ellerman <ellerman@au1.ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>