bhyve: Implement MSR_MISC_FEATURES_ENABLES

Linux reads MISC_FEATURES_ENABLES to manage the CPUID faulting feature
(undocumented in the Intel SDM, but documented in 323850-004 (Intel
Virtualization Technology FlexMigration Application Note). Since bhyve
doesn't emulate this feature, we always return 0. Neither does bhyve
support the MONITOR/MWAIT fault bit also in this MSR (which is
documented in the sdm), so always return 0.

Sponsored by: Netflix
Reviewed by: jhb
Differential Revision: https://reviews.freebsd.org/D36602