bhyve: implement rdmsr for MSR_IA32_FEATURE_CONTROL

Without the -w option, Windows guests crash on boot. This is caused by a rdmsr
of MSR_IA32_FEATURE_CONTROL. Windows checks this MSR to determine enabled VMX
features. This MSR isn't emulated in bhyve, so a #GP exception is injected
which causes Windows to crash.

Fix by returning a rdmsr of MSR_IA32_FEATURE_CONTROL with Lock Bit set and
VMX disabled to informWindows that VMX isn't available.

(cherry picked from commit 17d214c2ca9f110db3fa2a10d6b448d624e87774)