COMPMID-482: Refactor PMU counters

Change-Id: I9b254ce693363ecbbd7c188d211c85471134a91e
Reviewed-on: http://mpd-gerrit.cambridge.arm.com/84328
Reviewed-by: Anthony Barbier <anthony.barbier@arm.com>
Tested-by: Kaizen <jeremy.johnson+kaizengerrit@arm.com>
18 files changed