pmc.amd(3): rename from pmc.k8(3)

[mhorne]

Summary

This is step one in recognizing that the K8 microarchitecture represents
a small and aged subset of AMD CPUs supported by this class. Future
changes will update the code and documentation details to better reflect
this.

Keep the old filename as an alias.

[jkoshy]

Please consider a rename to 'pmc.amd.k8.3'?

[mhorne]

In D41279#940173, @jkoshy wrote:

Please consider a rename to 'pmc.amd.k8.3'?

Sorry, my commit description was maybe not clear enough in describing the "why" here. The K8 micro-architecture is long-retired, but PMC support for AMD CPUs remains nearly identical for the micro-architectures that have come since. Rather than creating, for example, a new pmc.zen2.3 page with duplicate content, I envision pmc.amd.3 to become the single page documenting support for all AMD CPUs.

[jkoshy]

LGTM.