Several files use the internal name of `struct device` instead of
`device_t` which is part of the public API. This patch changes all
`struct device *` to `device_t`.

The remaining occurrences of `struct device` are those referring to the
Linux or OpenBSD version of the structure, or the code is not built on
FreeBSD and it's unclear what to do.

Submitted by:	Matthew Macy <mmacy@nextbsd.org> (previous version)
Approved by:	emaste, jhibbits, sbruno
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D7447