KVM x86/pmu fixes for 6.6:

 - Truncate writes to PMU counters to the counter's width to avoid spurious
   overflows when emulating counter events in software.

 - Set the LVTPC entry mask bit when handling a PMI (to match Intel-defined
   architectural behavior).

 - Treat KVM_REQ_PMI as a wake event instead of queueing host IRQ work to
   kick the guest out of emulated halt.