We want to draw a firmer line between these. Both are supported by the
same PMC class (PMC_CLASS_AMD). However, the event sources are distinct,
with the legacy CPUs using statically defined events, while the Zen
event sources are the pmu-events tables. This has long been a source of
bugs and confusion.

Add some more internals to make this distinction real, by introducing a
new CPU type (PMC_CPU_AMD_ZEN). We allow for newer (Zen) CPUs to use the
old K8 events; but not the other way around.

Bump PMC_MINOR_VERSION for this.

Reference for AMD processor families:
https://handwiki.org/wiki/Engineering:List_of_AMD_CPU_microarchitectures