Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

- Extract the IODEV_PIO interface from ia64 and make it MI.
In the end, it does help fixing /dev/io usage from multithreaded
processes.
- On i386 and amd64 the old behaviour is kept but multithreaded
processes must use the new interface in order to work well.
- Support for the other architectures is greatly improved, where
necessary, by the necessity to define very small things now.

Manpage update will happen shortly.

Sponsored by: Sandvine Incorporated
PR: threads/116181
Reviewed by: emaste, marcel
MFC after: 3 weeks

Add ioctl requests to /dev/io on ia64 for reading and writing
EFI variables. The primary reason for this is that it allows
sysinstall(8) to add a boot menu item for the newly installed
FreeBSD image.

Use io(4) for I/O port access on ia64, rather than through sysarch(2).
I/O port access is implemented on Itanium by reading and writing to a
special region in memory. To hide details and avoid misaligned memory
accesses, a process did I/O port reads and writes by making a MD system
call. There's one fatal problem with this approach: unprivileged access
was not being prevented. /dev/io serves that purpose on amd64/i386, so
employ it on ia64 as well. Use an ioctl for doing the actual I/O and
remove the sysarch(2) interface.

Backward compatibility is not being considered. The sysarch(2) approach
was added to support X11, but support for FreeBSD/ia64 was never fully
implemented in X11. Thus, nothing gets broken that didn't need more work
to begin with.

MFC after: 1 week