This is a port of the bits related to vlapic-enablement of the following
bhyve improvement from illumos:
14598 bhyve vlapic should handle APICBASE changes https://www.illumos.org/issues/14598
A LAPIC can be enabled/disabled in two ways:
- by the global-enable bit in the APICBASE MSR
- by the software-enable bit in the APIC's SVR register
This change allows distinguishing between both forms of enablement where
that matters. The more involved changes to allow guests to modify the
APICBASE MSR are not included at this time.