Add support for Cortex-A76/Neoverse-N1 to hwpmc

This adds support for the Cortex-A76 and Neoverse-N1 PMU counters to pmc.

While here add more PMCR_IDCODE values and check the implementers code is
correct before setting the PMU type.

Reviewed by: bz, emaste (looks reasonable to me)
Sponsored by: Innovate UK
Differential Revision: https://reviews.freebsd.org/D25959