device_probe_and_attach.9: Document more device functions

Split out separate descriptions of device_probe and device_attach and
include extra details (such as the effect of a disabled hint during
device_attach). Reframe device_probe_and_attach as a recommended
wrapper function around device_probe and device_attach.

While here, add a description of device_detach.

Differential Revision: https://reviews.freebsd.org/D48364