Modification to support inclusion of pre-built virtio modules

Hi.

I have created a minor mod to the Makefile to copy kernel modules in module/boot/modules directory. (I used this layout because I can extract package like [this virtio modules][virtio] in the modules directory directly.)

[virtio]: http://people.freebsd.org/~kuriyama/virtio/

I also includes kernel configuration patch NKPT mods.