Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r230330:

Remove remnants of dev_t.

These functions take a `struct cdev *' -- not a dev_t. Inside the
kernel, dev_t has the same use as in userspace, namely to store a device
identifier.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

mdoc: order prologue macros consistently by Dd/Dt/Os

Although groff_mdoc(7) gives another impression, this is the ordering
most widely used and also required by mdocml/mandoc.

Reviewed by: ru
Approved by: philip, ed (mentors)

Use 'manual page' instead of 'man page' for consistency.

Approved by: re (hrs)

Update function definitions and required include files to reflect
the current state of the system.

Approved by: alfred

mdoc(7) police: Use the new .In macro for #include statements.

mdoc(7) police: minor style/formatting fixes.

Add vcount.9 / count_dev.9.
Touched up a bit and added some consistency to the text by your's truly.

PR: 23745
Submitted by: Andrew Stevenson <andrew@ugh.net.au>