bhyve: enhance debug info for memory range clash

Explain what the two clashing regions are.

Reivewed by: grehan, jhb
Differential Revision: https://reviews.freebsd.org/D29696
Pull Request: https://github.com/freebsd/freebsd-src/pull/463

(cherry picked from commit efec757b20425ac68171acc7f9cec8be750db688)