bhyve: add wrapper for debug printf statements

Add printf() wrapper to use CR/CRLF terminators depending on whether
stdio is mapped to a tty open in raw mode.
Try to use the wrapper everywhere.
For now we leave the custom DPRINTF/WPRINTF defined by device
models, but we may remove them in the future.

Reviewed by: grehan, jhb
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D22657