hwpmc: count each AMD PMC interrupt once

[afscoelho_gmail.com]

Summary

amd_intr() and amd_intr_v2() call pmc_ibs_intr() and then update
kern.hwpmc.stats.intr_processed or intr_ignored. pmc_ibs_intr() also
updated them. So each core PMC NMI was also counted as ignored, and
each IBS NMI was counted as processed two times.

Update the statistics only in the caller.

Fixes: e51ef8ae490f ("hwpmc: Initial support for AMD IBS")
Sponsored by: AMD

Test Plan

Run any sampling session, e.g. pmcstat -S instructions or -S ibs-op,
then read kern.hwpmc.stats.intr_processed and intr_ignored.

Before: intr_ignored == intr_processed.
After: intr_ignored stays 0.