os/os-dragonfly: sync with header file changes in upstream

os/os-dragonfly: sync with header file changes in upstream

IOCTLTRIM was moved and renamed to a different header file,
so conditionally include previous or current header depending on
__DragonFly_version.

Some details in below commit messages.
In short, they have had IOCTLTRIM in a wrong header, and they
decided to fix/change it since fio was the only application using
IOCTLTRIM within their userspace package collections.

<sys/ioctl_compat.h>: Add a reminder comment about IOCTLTRIM.
http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/7226e3530be4df743a5cfe61f602b0c4bd436ee9

Move the IOCTLTRIM ioctl to a better header and rename it to DAIOCTRIM.
http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/32506cfa691f80faa47486d6f94a98ae12387eeb

Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>