arm: perf: Add event descriptions

arm: perf: Add event descriptions

BugLink: http://bugs.launchpad.net/bugs/1559350
Add additional information about the ARM architected hardware events
to make counters self describing. This makes the hardware PMUs easier
to use as perf list contains possible events instead of users having
to refer to documentation like the ARM TRMs.

Signed-off-by: Drew Richardson <drew.richardson@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from commit 3fbac6ccb6c3a8958239d9026c4d41db60c2f1cf)
Signed-off-by: dann frazier <dann.frazier@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>