bhyve: add ioctl to modify the second level address translation

[corvink]

Summary

Second level address translation is used to create a mapping between
guest addresses and host addresses. In order to allow passthru of
mmio devices like a TPM, we need to modify the SLAT. Therefore,
add an ioctl for several modifications of the SLAT.

Note: You can take a look at https://github.com/Beckhoff/freebsd-src/commits/phab/corvink/vm_modify_slat

[markj]

lib/libvmmapi/vmmapi.h

190

Whitespace is inconsistent.

sys/amd64/vmm/vmm.c

649

This functions return Mach error numbers, for legacy reasons. They need to be translated to errno values before a return to user mode. See vm_mmap_memseg() for an example.

sys/amd64/vmm/vmm_dev.c

550

There is no validation that the HPA actually corresponds to a SLAT...?

[corvink]

sys/amd64/vmm/vmm_dev.c

550

HPA isn't part of the SLAT. vm_map_mmio should add it to EPT.

[corvink]

This patch was required for my TPM passthrough patch (D32961). I'll change the TPM passthrough patch in the future. After that, this patch won't be required any more.