[SRU][Bionic] Update ThunderX2 implementation defined pmu core events

[Manoj Iyer]

Please consider the following patch to ARM64 ThunderX2 PMU core events. The ARM architecture defines several events as part of the Performance Monitor Unit (PMU) Extension. In addition, Cavium has added "implementation defined" pmu core events, which Cavium deems most useful for analyzing performance. Currently perf does not list these "implementation defined" events.

The patch was tested by me on a Cavium ThunderX2 system and no
regressions were found.