If full width writes to the performance monitoring counters are
supported, use full-width aliases MSRs for writes. This fixes the
"[pmc,X] negative increment" assertion on the context switch when
clipped counter value is sign-extended.

Add definitions for the MSR IA32_PERF_CAPABILITIES needed to detect
the feature.

PR: 207068
Submitted by: joss.upton@yahoo.com
MFC after: 2 weeks