powerpc/perf: update attribute_group data structure

Rename the power_pmu and attribute_group variables that
support PowerISA v2.07. Add a cpu feature flag check to pick
the PowerISA v2.07 format structures to support.

Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>