bhyve: Move most early initialization into an MD routine

[markj]

Summary

Prior to initializing PCI devices, main() calls a number of
initialization routines, many of which are amd64-specific. Move this
list of calls to bhyverun_machdep.c. Similarly, add an MD function to
handle late initialization.

No functional change intended.

[jhb]

usr.sbin/bhyve/amd64/bhyverun_machdep.c

140

I assume arm64 uses the bsp?

[corvink]

usr.sbin/bhyve/amd64/xmsr.c

240

Nit: This doesn't belong to this commit.

[jhb]

usr.sbin/bhyve/amd64/xmsr.c

240

I assumed it was because now this routine is called by bhyve_init_platform which consistently works with errno values whereas before when it was in main() it wasn't necessary to be consistent.

[markj]

usr.sbin/bhyve/amd64/bhyverun_machdep.c

140

Yes, it sets the initial value for ELR in this function.

usr.sbin/bhyve/amd64/xmsr.c

240

Right, I was trying to normalize error handling at the same time.